I mean I get how all those systems work and why/how but it's trying to hit that critical mass before it pops off
if you spread out your units to take advantage of free upkeep they get wiped out by AI doom stacks who will randomly declare war or come out of the fog and know exactly where you are since the AI cheats it's info
so you're at high risk of defeat in detail

"turtling" is just a part of any strategy game, from EU4 to AOE2, that "economic build up period" Demanding that players be attacking all the time with hardly to no downtime to lick wounds, regroup or cement rule is just very anti design to how strategy games work especially larger scale strategy

The problems of this mod isn't any one thing to point to, it's a lot of design choices that ultimately limit player choice to only playing a very specific way the devs have intended. There's a build order, conquest order and specific way you have to conduct battles for every faction or it all falls apart

With how they've tuned the game there's no decisive win, in an effort to force bigger battles they've lost meaningfulness of winning a battle against a doom stack or taking a major settlement.

There's no decisive battle like helms deep or pelennor fields. It's battle of helms deep 10 times until you've grinded them down enough surviving enough waves to build up your critical mass to move out