Low-level wizards can still be pretty good if you get the Summoning skill and cast Summon Imp. Dropping an imp in the middle of the battle lines can cause some damage, distract enemies, and help control the flow of battle. The imp can fly over units, but the reverse isn't true - the enemy has to kill the imp to go through the space it occupies, which means they take damage and expends ammo, stamina, and turns. Don't forget the imp can shoot a ranged magic bolt one time, too. A warrior hero is definitely the strongest single unit you can reliably get, but also the weakest general. You can't pick off enemy units like a wizard or scout, and can't buff friendly troops like the commander. I have a commander that multiclassed into warrior (warlord) in my current game, and that works really well. The passive bonuses from the commander tree apply to all the units in your army, including the hero himself, so a commander is already somewhat tougher than average before you pile on warrior skills and heavy armor. In battle, Vlad McHerodude rushes the front and tanks like a T-64, while the regular units bring up the back and and form a main battle line.