Especially in the eastern theater, the Khuzaits are the force to beat (unless you ride with them). Historically, it was such such tribes and cultural branches thereof that would challenge and defeat Imperial entities like the Romans of Constantinople. Even long after they established themselves as the self-styled inheritors of the Roman Legacy, the Ottomans still hoisted the horse-tailed banner at the start of fierce campaigns. So you're basically fighting history itself as you try to stem the tide of Khuzait victories.
But if you can beat the Khuzaits, you can probably beat any other faction in the game with ease by comparison. The biggest hassle is that even if you take their cities, the AI lords will not do a good job of holding on to them. My plan, if I ever get around to it, will be to try retaining ownership of Khuzaits cities for my own fiefdoms. Chaikland would be a very nice place for me to set up shop