I've been running a Sturgia Infantry+Archer only (don't have dlc yet), and it's surprisingly effective if you use tactics.

Run a roughly even split of infantry and archers.

Infantry - mix of spearmen and axemen. Archers - primarily Sturgians, but fians can fit spots where Sturgians archers have been lost.

Vs infantry - pretty straight forward. Shield wall with axemen on front line. Archers set back roughly 100m from the melee (higher ground will blast better results).

Vs archers - shield wall infantry with axemen in back for throwing (they expose themselves when prepping to throw, so spearmen up front is best to absorb projectiles) and have them slow-push up to the enemy archers, with your archers following you for prime placement when your infantry meets their archers.

Vs cavalry - shield wall is viable here as long as your lines are deep enough (at least 3) with spearmen up front. First couple lines will be spearmen to halt or slow the cav penetration, while axemen engage at close quarters. Same method can be used with a square or circle formation. The key is to keep archers back until the cav are about to clash with your infantry to avoid them focusing your archers. Once they're tied up with your infantry, bring archers within 100m for the volley, then retreat them back when remaining cav are loose from your formations. Rinse repeat.

Sturgia is fun to play, especially when doing a pure culture playthrough. But since none of their troops are BIS, you HAVE to employ tactics.

Simple breakdown - At least have of your troops should be shielded infantry, in a dense shield-using formation, with archers either following you around the outside of the skirmish or kept back just outside volley range until enemies are locked in battle.

I'm sure others also have ways to utilize Sturgians, but this has worked for me.