Right now they are losing in my playthrough not because Vlandia has cav autocalc bonus, but because Vlandia actually bothers showing up to defend **** and will absolutely nuke a besieging army with 2x its numbers. I'm single-handedly holding off the Imperials and Khuzaits but I literally cannot leave the rough Tyal region because those villages supply my nobles and raiding from there down into Baltakhand supplies my warhorses and a modest dripfeed of horse archers (steppe raiders).
The rest of the Sturgians are just welping over and over and over into Revyl and Omor, never actually gaining strength before the Vlandian doomstack shows up to wreck them again.
I know that Ragnavad's AI isn't actually any different, but it feels like the Sturgian lords are as ****ing stupid as the worst sort of Viking stereotype you can imagine.