1) I haven't seen many wars with the Southern Empire, unless they manage to eat the Northern Empire's bordering fiefs. In that case, border tensions will obviously be a factor.
2) So I've been doing a few observational games (no player intervention) and simply watching Sturgia's fate. In one case, they are actually doing alright; mostly avoiding war with the Khuzaits and still holding their four far north cities four years into the game. That's decent enough, all things considered. The weakest faction is actually the Western Empire, with the Northern Empire having some issues and Vlandia/Battania going hammer and tongs against each other.
In the other cases, they actually held up reasonably well until one thing happened: they had an army get trapped in either the Tyal or Varnovapol corridors. A speed bonus wouldn't have helped in either case; the armies that came were much bigger and much slower but that didn't matter because there was no way out. Once they lost a doomstack to another, bigger doomstack, they were never in a position to recover because the enemy had effective control (not necessarily ownership) of some of their territory.
I write all that to say that an improved snow bonus probably won't help them much. When it comes down to it, there is only single entrances into Varno, Tyal and Revyl which means that any Sturgian force caught there has to accept the battle, regardless of their speed. Of course it cuts both ways, and Sturgians can trap enemies in their as well, especially besiegers, but those besiegers get to respawn back in their relatively safe holdings and try again.
The Sturgians have to win that contest every time -- their enemies need only win it once or twice to start the death spiral.
Really nice observations! I agree there is more to the issue than what many people tend to boil it down to.
I've been running some simulations where I shuffled up the wars that the factions are in on game start, and it seems to have an effect on the outcomes. I matched Sturgia up with the Northern Empire and Khuzait up with the Southern Empire, and those pairs are much more evenly matched. It doesn't result in one faction gaining an early head of steam that they can then use to power through a weaker faction.
For instance, I noticed that Khuzait normally would often take Amprela and/or Myzea early on then declare war on Sturgia at an inopportune time and quickly take Tyal, giving them a nice stronghold in the northeast portion of the map. Lord's would defect to Khuzait and they wouldn't have anyone that could really challenge them on their end of the map, setting them up for a snowball.
When you pit Khuzait and the Southern Empire against each other there's a lot more give and take, and Khuzait doesn't conquer new territoy quite as quickly. Sturgia is able to take some fiefs from the Northern Empire and are not caught out of position quite as badly when war is declared with Khuzait or Battantia. The other matchups in these tests are Battania vs. Vlandia and the Western Empire vs. Aserai.
I think under normal circumstances Khuzait usually benefits from having a lot of 'soft' targets nearby in the early game, such as Amprela, Myzea, Tyal, Husn Fulq, and a plethora of castles that are easily reachable.
I know it's only two data points, but here are the results from the two tests I ran past the 8 year mark (in 1.4.0):
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I'd love to see some other tests that try to measure the effects of things like starting prosperity and hearths (Sturgia is poor), types of villages local to a faction (Sturgia has medicore food sources), and whether or not passing the Noble Retinues or Royal Guards policies early gives a noticeable boost.
