One comes from a horse culture and the other does not?
That's a reasonable explanation for the difference in riding skill, at least. Strangely, the Khan's Guard has a T4 horse while the Vanguard Faris has a T5. The two horses have nearly the same total stats, though.
equipment is a big part of a units effectiveness.
This is also an interesting point. Khan's Guard has 51 head and 62 body armor; Vanguard Faris has 37 head armor and 65 body armor. Khans have a T6 glaive and a T4 bow; Vanguard Faris has (five) T6 javelins, a T4 one-hand sword, and T3 lance and shield.
The Khans seem to be objectively stronger not just in skills, but equipment too.
It's that everything about the Khan's Guard takes maximum advantage of AI and equipment imbalances and quirks.
Yeah. I don't get it. There are six T6 units. Two of them are hand-crafted to be OP in stats, equipment and AI synergy (Khans and Fians). Two are basically lame T5 cavalry (Faris and Druzhinnik). Two are pretty well balanced (Banner Knight and Cataphract). Is this supposed to be a difficulty curve between the factions? Khuzait is easy mode, Aserai is hard mode? Has Taleworlds simply been unable to find time for a balance pass in the last two and a half years? I wish I understood their thinking.