Why should Sturgia have such unfair advantages? And why should players who play other factions should be disadvantaged? Btw, 1.3 made faction traits functional, and those apply to all characters as far as I can tell, not just the player. Sturgian is +20% bonus to snow movement.
As far as AI battling each other go, "simulated" battles consider unit levels and whether units are mounted (a flat multiplier to level based strength of the unit card). Thus factions with a lot of cav and nobles get advantage in AI wars. Let's look at party templates.
Empire: 63 men total, 7 cav, 7 nobles
Sturgia: 53 men total, 3 cav, 0 nobles
Aserai: 50 men total, 5 cav, 0 nobles
Vlandia: 54 men total, 16 cav, 10 nobles
Battania: 53 men total, 12 cav, 7 nobles
Khuzait: 57 men total, 19 cav, 0 nobles
I feel like there are indeed some factions here that have unfair advantage but I'm not sure if Sturgia is one of them.
Now let's do players. There is an obvious hole in Sturgian troop tree, their top tier archers have low tier bows and arrows and mid tier medium armor. They aren't comparable in any way to tier 5 ranged units of any other faction. Are there some other units in the Sturgian troop tree that justify their ranged being trash? Druzhinniks are basically Vlandian knights but slightly worse due to some questionable equipment pieces and are a pain to upgrade because they only get a horse at tier 4. Veteran warriors are good but hardly better than legionaries and sergeants. That leaves us with shock infantry and skirmish cavalry. I really doubt those are great enough to pull Sturgia up by its bootstraps.
Obviously, as a player in all your wisdom, you can lure the AI into attacking your shield wall and play as Sturgia in that way. You can also do it with any faction. In fact, every faction will be better at it than Sturgia, even Khuzaits on foot. Their ranged units will just slaughter half the enemy army by the time they get to melee. Empire and Battania won't even need a shiled wall, they can spam archers and win every time.
Sturgians get -20% to snow penalty, not + 20% to movement in snow. If the the penalty itself is 20% then the effective bonus is +5%. Is the penalty itself even implemented by the way? Meanwhile Vlandians upgrade their already bs knight armies 20% faster and Khuzaits get +10% to movement bonus from cav everywhere on the map. I certainly hope that these traits don't work for AI parties because it would just exacerbate the issue if they do.