Another idea to make human heroes more useful: built-in "heroic luck". Let's say your regular hero fights in the battle, takes a big hit and dies. But when "heroically lucky" hero fights and takes a big hit he only kind of dies - he isn't anywhere on the battlefield and he doesn't participate in the battle in any way, but if your army wins you'll get a message that as the army returned to the camp hero "such and such" appeared out of his tent cursing that some prankster stole his armour while he was sleeping
