Agreed, it was way better in every way.
I'd also add they should reintroduce the army gathering mechanic AND force them to spawn at their own vassal's capital counties, to avoid exploits (IE: Have a kingdom on the other side of the map having a single county next to the frontline to spawn all of it's armies over there).
The game was a chore early on but after a few QoL o changes gathering an army was mostly automated, the only difference is that the shape and size of your empire actually mattered as your armies could be intercepted before they could gather together, and this should return.
If we add the fact that armies can simply walk into the sea in CK3 even english levies shouldn't cause issues to the mainland.
Another change I'd make, since every single little levy had it's own banner, the sub commanders leading those banners should replace knights, that or make knights actually have their own retinues, instead of pretending through text, either using the CK2 custom mercenary company system or the new adventurer system, make them raise, train, upgrade and replace actual soldiers instead of acting like space marines that ignore atrition.
Hell I really wish they'd add back flanks too, and tactics, and the actual combat phases that matter to the battle mechanics.
I'm of the opinion that retinues were a mistake in ck2. Levies and their source made sense. You build stables, you get cavalry, you build barracks, you get heavy infantry, etc. Retinues were just... spawned out of thin air, glorified mercenaries that function as a standing army several centuries before the first post-antiquity standing army was even possible in OTL. The AI couldn't handle it, the player gamed it. Worst of all, it threatened to undermine the levy system for which the core game mechanics were balanced around. I ended up avoiding the system altogether like a plague.
Men at arms in ck3 suffer from the same problems, except now we don't even have a proper levy system. You have to use men at arms, the whole battle system does not exist without them. Meanwhile levies are useless and thus so is every source that provides them.
What they should have done was throw out retinues altogether. You shouldn't be able to pick and choose your armies just like that. The only source of armies should've been buildings, just like in base ck2. Buildings represent the logistics behind the scenes. It takes time to breed proper warhorses, to train archers or to smith weapons... Just how nonsensical is it that in ck3 there is a blacksmith building which you don't actually have to build to provide weapons or armour for even the heaviest of troops? One should be necessitated to build the means for fielding an army to be able to actually field it. The 'economy' side of things should not feel detached from the army side of things — and no, providing space marine bonuses is not a proper subsitute.
I agree, the idea of retinues/MAA was decent on paper but they trivialized a lot of content even back in CK2, levies made sense and your power came from your land, your vassals, and how much they respected you.
After retinues were added players could survive the entire empire revolting against them by just moving around and wiping their levy stacks before they could gather in significant numbers, it didn't quite break the balance in CK2 like MAA did in CK3, but it certainly made things worse.
Then theyd have to admit the change was a mistake
And then they'd have to admit another change was probably a mistake too.... And another... And another....
Very little of what we used to have was changed for the better tbh, I can only think of culture and maybe nomads, I'm not convinced on clans, diseases and anything related to warfare were very clear mistakes and I don't think the modular nature of CK3 religions made the game better, everything feels generic and of little relevance compared to the strict, game-changing religious differences of CK2.