DsRaider, i play with 9 ai factions, i don't wanna increase it more because at the moment the Huge maps is still too small for me
And no, a hero isn't just sitting there.
You can have a troop unit or a hero that sits there but as it levels up with ur army, it will keep it well healed, high level First Aid is powerful heal.
Sometimes a low level hero can be a difference between you still getting to keep every single unit on field because of first aid/healer while an army with no hero will lose several units.
If you're clearing an area full of monsters, and it's chockful of powerful monsters? You will need to bring several armies to that area just to clear it out fast in same amount of time where it might just take two armies led by a hero each.
And an commander skilled up in accuracy increase will ensure your soldiers don't cry to their mommies when it face hyperdodge resolns with full dodge upgrades
Commander = Force multiper.
Assassin = It makes things dead.
Mage = Magical Damage and Aoe.
Defender = sit there and look pretty, its only hero i haven't played much with yet.
Warrior = it beats thing until they look bloody and dead.
Out of all hero types, I use commander the most.