First off, I perform my testing while playing as Harad. I am mostly concerned with how the 'Good' factions interact with eachother and how the battles between good and evil pan out. I believe Harad to be the best choice for this type of testing as they can fairly well isolate themselves from the rest of the battle. During testing, I expand to my natural borders (you'll see in the pictures) and then continue to play defensively against Gondor (I don't cancel the war, so as to simulate the continued battle between AI Gondor and AI Harad).
Note that there is of course room for variation from one campaign to another, but using my aforementioned testing procedure the results were atleast somewhat predictable.
Now, on to the pictures. Here's a sample picture of the campaign map using my submod (the YesEco version, which contains adjustments to the Kings Purse for some factions). Here we are at turn 10 in a campaign I'll use as an example:
Gondor and Mordor are fighting it out over the river settlements. Mordor has captured those on the east side and Gondor on the west. All factions have expanded to some degree on a fairly even scale (remember, the goal here is to achieve a relative balance between the factions as they expand). At this stage, Gondor is being generally reported as one of the top factions, as it starts out with the most settlements overall and a reasonable military position. Mordor occasionally gets reported as the top faction in Military and/or Production, as the armies of Sauron begin to grow...
Now it's turn 20 in the same campaign:
The factions are starting to fill in the gaps, expanding relatively equally with no factions either overly powerful or weak (or destroyed). Both of the elven factions are doing reasonably well, especially considering that at this point (without this submod) the Silvans were often wiped out by the combined forces of the Orcs and Mordor. The High Elves still hold their capital (which is typical) and you sometimes see expansion to the northwest or southwest from their capital (not this time though, as they have instead expanded along the western coastline). Rohan and Isengard have not yet gone to war, but it typically occurs between turn 15 and 25. Before the war begins you'll notice Isengard often reported as a the most rich faction, as they build up their wealth in preparation for the inevitable war.
Though not apparent, a rather vicious battle is ensuing between the Orcs of the Misty Mountains versus the Elves, Dwarves and later Eriador. This is typical, and the results rely heavily on how well the good factions involved work together. In this campaign they do a pretty good job of working together against the Orcs, but some of the test runs showed the Orcs gradually gaining ground when the forces of good were less organised. The battle between Dale and Rhun is going slowly at this point as they continue to capture the last couple rebel settlements (at which point the battle usually gets a bit more serious). In some test runs the Dwarves come to the aid of Dale and Rhun gradually gets pushed south, but other times Rhun continues it's push into Dale's territories. This particular campaign see's a fairly even battle between them, with the Dwarves too focused against the Orcs to bother to join in.
The neverending battle between Gondor and Mordor is still being fought over the river settlements between them. Typically this is where their battles will be fought up until between turn 35 and 45, where the forces of evil begin to push forward. Gondor is indeed a strong faction at the beginning, but in the early stages of the campaign they generally have to fight alone against the ever growing hordes of Mordor. This leads to a gradual push into the lands of Gondor as the game goes late, culminating at the inevitable battle of Minas-Tirith. A strong alliance between the good factions can make a difference here, but the other factions generally have their own wars to worrry about.
By turn 50, you get a better picture of what this mod is hoping to achieve:
All of the rebel settlements have been taken. A good balance has been achieved between the factions, with none left behind or expanding too fast. Mordor is still the powerhouse it is supposed to be, and left unchecked, with continue to expand into Gondor, sometimes Rohan, or North against the Silvan Elves. Mordor is still as strong as it was before, actually stronger (due to better performance of the good factions in general), slowly expanding into the good territories as the game progresses. I chose to keep with this aspect of the game, as it sticks with lore and the general theme achieved by TA:TW.