I'm torn on this one. I actually like the notion that an undefeated army becomes a fearsome sight on the campaign map. I came across a serially victorious Derthert, and taking down a high tier Vlandian army felt like one of those epic moments that punctuate an exciting campaign. It's really interesting to me that you, and so many others, highlight Khuzait. I really think the high-tier army problem is specific to Khuzait:
- Their movement speed advantage: Both from high cavalry usage, and a broken cultural trait that gives +10% of 'Base' movement speed rather than +10% only to the cavalry component. Can anyone confirm that the AI does in fact receive the same culture bonus as the player? Even with stacked horses in your inventory, as the player you'll often struggle to catch up to retreating Khuzait armies. They'll always pick their fights rationally, and as such do not experience the normal frequency of army resets that other factions do. For the AI, that doesn't know to stack horses? They'll only ever get engaged by Khuzait when they're near-guaranteed to lose. Ergo, predictable map evolution and army strengths on the Eastern front (somewhat contained, in fresh 1.4.1 playthroughs on main branch, by what feels like a hidden coalition mechanic to contain anyone climbing much over 20000 faction strength - but that's another topic, unrelated to this thread).
- The horse archer problem: Archers are your main damage dealers in Bannerlord (2 quivers worth of safe damage, plus forcing the engagement on your terms - nothing compares). By virtue of mobility, cavalry survives way longer. Put heavily armoured archers on heavily armoured horses, and you get the most devastating unit in the game. Given their troop trees prioritise cavalry and archery, you'll suffer more casualties facing a high-tier Khuzait army than any other.
TL;DR : I'm not sure I mind the occasional high-tier army so much as I mind the specific conjunction of Khuzait too easily developing high-tier armies, and their high-tier armies being the best in the game.