I think (Broadly i can see your point and agree with much of it) another factor though for a new Tory leader, that would directly effect Corbyn's chances is who exactly it might be. Indeed a new one can remove May's negative appeal and strike a blow at Farage. However the candidates to do that (and the ones most likely to win by the bookies- Boris for instance) aren't unifying figures for the electorate. The front-bench all come with their own issues, but a so-called 'hard brexiteer' as PM while taking the steam out of Farage, would not make up the ground lost to Corbyn (and the Lib-dems, who i hasten to add isn't quite clear, but i suspect polling-wise its Conservative remainers/Conservatives who disagree with domestic policy and its impact, but who of course will not vote for Labour). A Boris, or Boris-like Tory leader will essentially see the vote share between the Conservatives and Labour remain as now (Not polling-wise, but as it stands), giving at best minority governments to Labour or the Tories. The key here would then be either the Lib-dems (how much vote share have they hiked off from a Boris-led Conservative party, who Tories have said if he or a 'hard brexiteer' takes the reigns they'll oppose/even split from).
Of course there are 20+ candidates all running for Conservative party leader, and as we saw last time, the favourites can suffer quite random disasters or mistakes that propel an odd-ball to the position. But given the Conservative party members favour a Boris-type candidate, its a situation that is foreseeable. Its unlikely for instance a 'remainer' will be PM as things stand (Unless of course the Conservative party in its internal voting makes sure to kick the 'controversial' brexiteers off the ballot prior to party members having a say), and its questionable whether a compromise candidate can really...well compromise.
Corbyn indeed has more variables on his vote share due a wider choice of left wing parties, but i think given the 2017 election his 'core' support doesn't stem from brexit at all, but the domestic case. The current rise of course is brexit-related and Tory meltdown related. However, the lib-dems in current polls at least seem to have gotten their momentum not from Labour supporters, but directly from the Conservatives, so with Lib-dem and Brexit party, and even the remains of UKIP (Who even if they've got very few to no seats (I.e. UKIPs outlook particularly for the latter) as i'd currently expect, will still split the rights vote share in key constituencies) there are equal options that while not taking the Conservatives down radically, might get Labour the minority government (or majority). What's more coalition between two parties (Lib-dems and Labour) is something i could see (Not coalition of course between more than that, it would be far too messy for the Political system, so the so-called 'Progressive alliance' is rather a pipe-dream of the lib-dems).
A big factor for the Conservatives is Scotland. It essentially allowed them to have a minority government by gaining MP's there. The question of course is if they can hold their new seats (Which is unclear given current controversies, and also the simple fact that the Conservatives were voted in potentially because during 2017, Labour, the traditional party of 'Unionists' in Scotland had been written off as dead under Corbyn. So if you wanted to protect the Union from the SNP, you'd essentially only have Conservatives to turn to who had the power to ensure that- this time around, the shoes on the other foot and brexit might feature more prominently- If you want to remain in the EU, but don't want to leave the UK- Labour makes the most sense, despite being rather complicated in being mostly-leave, and a second referendum in certain cases).
Indeed, i think though the issue is that the 'moderate' element in British politics is absent still, Biden if i'm right is essentially running on 'back to old securities and some social reform'- This is the Lib-dems and Change UK, but their vote share currently is not holding up, and it looks like Change UK through their failure to even have the bravery to challenge the other parties in bi-elections might just die out. The Lib-dems though have also sucked in voters from the Conservatives and even without momentum, Farage will become a 'UKIP mark 2' which does effect the vote share potential of the Conservatives, even if it gets them no seats. This i would add is me still assuming an early-snap election within current conditions. 2022, I think we'll be back to 2010 with the Lib-dems essentially slightly large at the expense of Conservatives, Labour going back to its 'core' share and the same with the Conservatives, so it being a case of 'who forms a coalition with Clegg 2.0 first)- its a long-shot guess though. It depends to what extent brexit or post-brexit is utilized as a political football and what a post-brexit Tory party does for A) leader and B) about the domestic economy- theoretically speaking, all they need to do is co-opt the basis of Corbyn's platform- reject austerity and release the spending flood-gates to schools, NHS, local councils, Universal credit, infrastructure and actually create an industrial strategy that has levels of state intervention- that they would do this is just today they are renationalizing probation officers (Baby steps, but its huge ideologically showing that 'One Nation' Tory roaring back to life). The question is if they could expand this to other areas (Unsure honestly ).
Farage by having to economic platform indeed is doing well by being so streamlined- one message, but this won't cut it at a GE (Though reading back, apologies as it might be you were exactly talking about the EP elections and not a GE, i'm still in morning mode!). Its an element that will have major impact at any GE, even a snap one- what will he do about the domestic scenario. Otherwise he's in danger of the Tories mistake in 2017, to make a snap election about brexit, while Corbyn campaigns solely on the domestic. To highlight for instance from July 2018-
https://ukandeu.ac.uk/new-polling-re...-the-priority/The overall importance of the UK controlling its own laws held true for both Conservative and Labour Leave voters. Issues such as pressure on public services, housing or jobs and wages came much lower down in ranking (7th and 8th).Economic growth is most important for the whole population – not sovereignty
There is however no overall majority for Hard Brexit outcomes, given the UK Government’s own assessments that Hard Brexit would adversely affect economic growth.
Remain voters favour strong economic growth over control, trade deals and immigration by very large margins (77% vs 23%; 79% vs 21%; 84% vs 16% respectively). So, although a majority of Leave voters do prioritise Hard Brexit, the closeness of the referendum result meant this does not translate into a majority in the country as a whole.
The top ranked priority overall was ensuring that the UK has strong economic growth, with a majority of people believing this was more important than the UK having control over its laws and regulations (54% vs 46%), being able to strike trade deals outside the EU (59% vs 41%), and reducing immigration (66% to 34%).
Since the majority of the electorate from all sides are domestically-concerned, its not enough at a GE to not have coherent policies and make this a central piece of their platform. Labour's strategy has been currently trying to essentially 'avoid'/cut through (depending on your interpretation) the brexit debate and reach out to voters on this issue, its still an important one as perception and reality in the media and among voters have this as a daily issue. Farage unless he has his planning spot on, could (as in fairness a new party might) fall to the Tory fiasco of 2017- try and make it all about brexit, rush the economic and domestic policy- so that you either choose one that is unpopular (if Farage keeps to a very libertarian agenda, he might not though, he is pragmatic) or one that has a lot of holes in it, or can be 'spun' as having a lot of holes in it (I.e. Dementia tax for the Tories in 2017- it wasn't necessarily the 'mad' idea Labour and co made it out to be... but it was flawed and able to be exaggerated effectively). So for me, its a definite that until Farage unveils his domestic platform (which he said he'll do following the European Elections), he's too much of an unknown to comment effectively on his GE impact (which has as you've pointed out indeed a lot of other issues as well for him).
Beyond i will say as a certainty, that unveiling an economic platform will see a decrease in current support levels (When you have Anne Widdicombe and George Galloway as both supporting you, your going to have issues keeping your voting group united ), which was Farage is sensibly holding the manfifesto and domestic platform until after (https://www.indy100.com/article/nige...ifesto-8883971) the EU elections, so it doesn't divide his party, as he will have to work to campaign and rebuild support (if he can at all- a Liberatarian/Manifesto similar to when he was UKIP leader did not and does not go down well).
In regards to the second referendum question- i've posted a bit on this in the 'long post', but just to summarize- Yes their will be damage to credibility of democracy, but the Westminster system does not rely on that to function, it merely requires the support of certain small key groups, and apathy. Brexit just isn't a 'big enough' issue for if Parliament decide to hold a second referendum, their to be much change- Violence actively generates support for the government (even an unpopular one), and nor are their enough brexiteers willing to go that far (Indeed quite fairly a lot have stated they simply would never vote in a GE again- which suits Westminister system to a T as its designed to arguably function better with fewer active voters). The key fact to bear in mind throughout all this is that the Leave vote won the last referendum by mobilizing around 3 million voters who had never engaged politically before, Remain had discounted them due to this- but Leave extraordinarily (and its a very commendable and politically savvy feat). A second referendum (or indeed for Farage a GE- an added factor) its not a sure-fire thing they'll continue to turn out and vote, especially if the one time they voted, was ignored/discounted. Even if they do, the other parties and 'remain' have been shown not only do these people exist, but they need to target them. So the advantage is no longer there- its also partly why those pushing a second referendum, i'm not buying the arguments of 'democracy', but its a pure Power Politics play as they believe its highly likely they'll win. However because of the factions involved (and the indeed the Leave faction of 'hard brexiteers' while currently more coherent, are not a majority- so a Second Referendum would indeed cause issues- not to mention the question would most likely be May's deal vs Status quo (and maybe vs WTO- but that splits leavers potentially for the government) by being a binary choice, likewise a GE with its added layers of domestic complication would also see this voting group fracture (going back to why Farage sensibly keeps the domestic off the agenda for now)- so it'll suit the EP elections indeed, but i'm not sure the extent to which it might hold up.
Again though, this is just my current thoughts, subject to change . I think though the long-ball i would throw is that currently, providing brexit is 'done' one way or another by the summer- it will still remain political football that has polarized an electorate in an unfavourable way for those who carried it out. Farage i can't see once the domestic agenda is put forward maintaining his momentum (Unless the Conservatives decides they no longer themselves deserve to exist- though even then, depending on platform, but if Farage continues his traditional economic platform, it will not get anywhere ala UKIP). Corbyn will go back to his 'base' (which will be large than the Conservatives due to natural voting shifts, though these 'young voters' who are pro-EU might go over to the lib-dems potentially if the UK's post-brexit relationship can be spun as political football) vote share, the Conservatives depending on leader and policies may have seen further losses to the lib-dems (as they are now seeing), but i can't see Farage having the momentum he currently does to this point, it'll essentially cease and the real fight will begin upon his domestic take (and depending on if the Tories indeed come up with a leader who can take him on). So i can see a Minority Labour government, or coalition potential as we had in 2010. The circle is complete . That's all subject to change, but just where i'm thinking long-term.