Bit o' a rant here: but the way the Venice faction is represented in-gane is absolutely bonkers.
Venice, which was historically home to the MOST advanced firearms production industry in all of Europe, and INVENTED many cannon types, can't even build Basilisk cannons...
https://en.m.wikipedia.org/wiki/Venetian_Arsenal
The Venetian Arsenal was also the most advanced center for shipbuilding in the world through much of the Middle Ages: yet Venice can't build Admiralty buildings (or a renamed equivalent) and thus gets no natural bonuses to ship production costs: which was one of the most important benefits the Venetian Arsenal offered (ships could be built very quickly and cheaply).
Their trade, meanwhile, is actually a bit WORSE than that of the Holy Roman Empire- which gets not just banks, but Printing Presses (which help with trade), and has a much larger starting-empire to trade across as well as easier avenues for expansion: including, notably, not having a terribly hard time rolling into Venice using Bologne as a staging-point eventually if they're able to hold onto it long enough (if played by a human player, of course: the AI is easily thwarted just by spamming Italian Spear Militia...) although it admittedly is a pretty hard siege battle (due both to high-quality Venetian militia and the inability to siege the city from more than one side) and may require starving the Venetians out...
Thus, Venice is forced to engage in extensive diplomacy with everyone to survive (well it would be: assuming the AI weren't so incompetent in battle and I wasn't a military genius in real life as well as being good in this game, who only didn't make it in ROTC due to medical clearance and very underdeveloped social skills in my early 20's...) as it can't even hope to affordably match the Byzantines at sea, the HRE on land (who make up for lack of quality with massive quantity: again, huge starting empire with good expansion prospects), or deal with psychopsthic Sicily betraying it every few turns (no matter how many Alliances you sign, even at "Perfect" relations, allied, with a drastically superior Power rating and high Reputation, they still backstab you repeatedly... The game dev's took "never trust a Silician" just a tad bit too far in their AI design... ��)
And while Diplomacy is GREATLY improved in Medieval 2 vs. Rome Total War (as are some aspects of city management, economy, and military balance) it's still one of the most boring aspects of the game: especially when you're trying to bleed the AI's for every last Florin they're worth (1) so they'll have less money to raise armies against you, (2) so you can bribe them into the Alliances necessary to keep your reputation up and survive without having to constantly fight battles against superior forces (which again, I could do in my sleep. But it gets old after a while...) and (3) so you can build up the kind of killer economy necessary to actually conquer foes like the Holy Roman Empire and end their menace once and for all, and then be able to defend their lands from the Poles, Danes, and Mongols without killing your economic growth in your core provinces, or having to rely on sheer tactical brilliance and overwhelming victories .. (the Byzantines, despite being an absolute menace at sea, are easy enough to conquer as Venice if you just want to win the game quickly: as they drastically under-invest in their armies, don't adequately defend any city but Constantinople, and have an economy that really is far too weak and underpopulated considering how strong they still were economically by the 11th century, historically, even if far less so than at their peak...)
Now, I make it sound a lot harder than it really is: after all, I'm a skilled Total War player, and in many ways (starting with such a highly defensible Minor City, their GREAT early militia spearmen, the ability to train not just infantry: but militia cavalry and superb Pavise crossbows in their cities) Venice is "easy mode." But I'd much rather if the dev's had better represented their strengths (amazing firearms, and naval shipbuilding at a very low cost) and just made the Holy Roman Empire and Milan bigger menaces at the start to compensate... Say with stronger starting armies in Italy, and more economic development to pay for them (most starting settlements don't even have basic Land Clearance: what kind of BS is this? Cities in Total War games always start FAR too underdeveloped to be realistic- this was a problem in Rome as well: where the Greek cities, famous for defeating the huge Persian navy at Salamis generations before, couldn't even build triremes yet at game-start, some lacking even basic ports... Which was hilariously bad design: as Rome could basically steamroll all of Greece at game start, rather than the generations of economic development in Italy and territorial expansion it historically took for Rome to be strong enough to face them head-on...)
I'm not saying Venice is HARD: Milan can easily be wiped out in an early attack if you don't mind upsetting the Pope, or move quickly to take their cities before he can demand an end to all aggression; HRE has their emperor worryingly isolated in Bolonge at the start- and the city can be easily surrounded by a larger force of Italian Spear Militia and taken in a well-contested assault, then ransomed back to kill him if the HRE is too broke, or recover the Florins necessary to do all this- the cost of which will slow down your early expansion in other directions: like to Corsica/Sardinia, and rapid economic growth, a good bit...
BUT, Venice is far less powerful in some ways, in the mid-game, than it should be... (and also, often much more of a land power than it historically was: but this is also because players are typically much more aggressive in conquering than Venice ever was).