Well, the factions have much better starting economy, positions, and basically dont have to upgrade buildings/settlements, dont need to take any rebel settlements, compared to Aow so even with similar ways to limit economy as in AoW, the factions would still be able to field many more armies than in AoW likely .... Also keep in mind that this mod has insane amount of generals

, hence their upkeep was lowered to basically nothing (to avoid them all going bankrupt), so all factions can field about a stack or two of generals, who are basically for free

(though on other hand the regular units are pretty expensive...)
... so army upkeep + partial/full removal of army upkeep would likely be the best way ... (plus we shall ofc keep the financila rules)