Yes currently mercenary troops are less in numbers and only avaliable at towns and mostly (50%) level 11 watchmen. I was thinking similar solutions with what you offer. Mercenaries should be more important at game and especially rich kingdoms must easily increase their party sizes with them to recover after losses. Will think some improvements in these issues.
Well but the problem is, that Sturgia isn't really "rich".
I saw them hire mercenaries when they got steamrolled as usual, but obviously not enough, they got steamrolled in my current playthrough as a Battanian Noble, their last city Sibir has fallen.
I'm not sure, since this is the first time I see a faction get erased, what happens now, if the remaining noble parties (I saw them) must be eradicated for the faction to cease to exist or if they decide to jump ship and just join other factions.
Regarding Sturgias Background story, that Nord mercenaries chose to live in that land together with Sturgian "Natives" (which in Warband are most probably the Vaegirs), it would be cool that if Sturgia falls, some time later, like a Viking Conquest, Nord Armies land on the coasts in the north with new nobles with large numbers (like 5K in total so they pose a challenge), declaring war on any kingdom that occupies Sturgian land.
Anyhow, that solution, although it is a good one, wouldn't solve Sturgias difficult geographic situation.
However I understand that you don't want to touch the map as of now and do a major overhaul of it, probably you regard it as finished.
So here is a solution I can think off:
-Give Sturgia more nobles with a full party at gamestart with atleast a majority of Tier 2/Tier 3 troops, that should help balance them, so they don't get immediately steamrolled.
-Let Sturgia start with the policy, were recruits replenish faster but they earn less taxes (forgot the name of that policy) and one or two other logistical laws that helps them.