Actually, I compared sturgian t3 armors with battanian and vlandian - and they're, surprisingly, on par. Battanian Trained Warriors have about 5-6 more BA, but they still lost to sturgian soldiers in a 100v100 (Enhanced Battle Test mod). Which, I believe, wasn't the case about a year ago, when I was digging into this matter last time. So sturgian regular infantry is not in that bad of a place these days, but yea smth a bit better than a scarf wouldn't hurt. Heavy axemen are actually good enough to beat legionaries most of the time and even vet falxmen - mostly thanks to their initial jav volley in both cases (which apparently does not happen in the youtube video you mentioned, it seems the author tests melee only). Heavy spearmen are confirmed garbage tho - I had doubts about how they perform against cavalry - they don't brace their spears and just don't perform against anything at all.
Varyag vets confirmed to lack skills in comparison to their rogue counterpart - chiefs are significantly better in 1-h, throwing and athletics and also occasionally have fur cloaks, when vets occasionally have scarves.
Druzhinnik Champions consistently lose to Banner Knights and Elite Cataphracts but are on par with Vanguard Farises (usually wining). Maybe a heavy lance wouldn't hurt tho, but in that case banner knights should get a longer one too.
And yea, general cav AI is retarded, any cavalry performs better with RMB battle AI (didn't like the mod's weapon and troop overhaul, but thankfully these two come in separate modules). On the downside - this AI complicates things too much for shock infantry with throwables - like breakers and falxmen - these just keep throwing their ****ty axes till they run out of them instead of closing in asap in order to do what they're actually good at.
Now, about those Khan's Guards. Yep, they're way too good. Yep, all thanks to glaives. Not only KGs actually, but starting from Torguuds and up. Even khuzait T4 noble units dominate anything. Only Elite Cataphracts got them routed for the enigmatic reasons of how morale works now - body count was still well in favor of KGs. So it's not about armor or skills or horses - only the glaives.