I think I have to agree on this. Also you have to consider that cavalry heavy armies move faster on the campaign map. This means that Sturgia is often facing armies that move quite a bit faster then they do. That is a huge advantage since often even a smaller, non-cavalry based army, can be easily overtaken by a large cavalry based one. Also it is easier for cavalry based armies to outrun the opponent when they can't win the fight. All in all this means that cavalry based factions tend to find themselves at the advantage for most of their fights.No, the reason why battania is doing well is because they're the 2nd largest calvary nation and their towns are very close to each other. Mounted units get a bonus in auto resolve (ai fights). Noble units barely matters for ai given their rarity. Sturgia is weak because they boarder the two best calvary nation while having inefficient pathing between their own fiefs. I'm all for having huscarl units but if they replace a mounted unit, it will weaken Sturgia further.
Also your right about how much geography makes a difference. Sturgia is literally hell to try to move through and it takes a long, long time for lords to move from one end to another. Also they have to mostly move down a narrow valley between to sets of long mountain chains making it easy to intercept lords.
Battania however is super tightly clustered so all the lords tend to be bunched in one place and can easily form armies and or react to defend towns and castles against sieges.