I respectfully disagree with this. While the Battanian volunteer is clearly the best tier 1 unit (because they have the mallet) Sturgian troops are among the largest troops and so more likely to hit the head you just either have to use loose formation or have them ambush from behind the top of the mountain so when the battle starts they already closed the distance and have the high ground. They also do better than volunteers in close quarters which makes grouping them into a horde and ambushing effective.
When they get to tier 2 the warrior has a very strong helmet and round shield. The warrior was recently buffed (before he just had a fur hat and now he has an 18 armor helmet). The warrior is very good especially if you have a good infantry captain, what I do is mix warriors and woodsman maybe like a 60-40 ratio and have them in shieldwall on high ground along with some Otroks. They warriors hold the shieldwall and the woodsman will throw javelins (they can all be in the same formation)
If you have to be offensive I find it is best to just put the infantry and archers together in a good formation with a good captain who has the flexible fighter perk and have them sneak around a hill and just swarm the enemy. Sturgians usually win if you dismount all your cav and put everyone in one super formation with a good infantry captain because you have all the critical mass in one area and because the archers have a good helmet and shorter range bows they tend to do better hanging around the infantry and shooting the closest thing for critical mass and you always need a few archers to shoot fleeing enemies so infantry does not waste time chasing them. If you play other fantasy games or what I would look at the sturgian archers like orc archers or something, they are kind of crude and lack skill but they have an axe and good armor and seem to do best walking around with the infantry. I did try a Vaegir like run where I got a really good bow captain and my all my family/companions into sturgian fians and they actually do good as long as you get the range right and guard them with spearman (they don't have longbows) in that way they played kind of like rhodoks
I would also recommend getting line breakers. You need them to fight larger armies because they can cleave multiple opponents with the axes and at 150 skill with a better handling captain (its only level 25) they fight with at least 180 skill which is like the average noble and they will destroy enemies even if outnumbered.
I also go with the heavy spearman over the axemen because they come with more skill and better armor and they have a 160 length spear which is perfect for both stopping cav and being short enough to be a good fighting spear. If you just want one troops type and want to be more general than I would opt for axemen, they have less skill and armor and are more of an all rounder general unit for sieges or anything but I prefer the higher skill units so my army is mostly heavy spearman/axemen/veteran archers and noble line and I take all the perks that boost combat skill
So my low tier comp is like recruits that either sneak around a mountain and blob or charge in a loose formation.
Middle tier is warriors, woodsman and otroks who use a spike shield strategy or just form a great horde again
High tier is heavy spearman, heroic linebreakers, veteran archers, noble line, all cav dismounts and joins one superformation and they
just form a blob and with a good infantry captain and medic on realistic difficulty they defeat larger armies with few losses
I usually don't recruit the brigands or upgrade to them but if I happen to have some I usually either have them join the super formation, charge them out to screen to distract the enemy for a safer approach or just hold them back and use them to chase routing troops