In my oppinion the gap between champions and regular units is caused by the level difference and the amazing gear they can get from quests or monster looting.
If i replace the assassin blade with one of the swords regular troops can use, my unbuffed lvl 24 warrior is no longer dealing over 100 dmg/hit to the best enemy troops. He stil wins the fight (quite easily i think ) but he needs 3-4 turns to kill a unit instead of just one.
If i replace his armor (with average armor not the best available for regular troops) he might lose vs several packs and for sure he won't be able to wipe complete armies one after another.
Even with this gear the toughest monsters I've met so far are kill-able. I might need to use some buffs and more troops and maybe even lose some of the regular units but imo those fights will become better this way.
I know removing extraordinary gear will diminish the excitement of exploration and monster fighting but something needs to be done to decrease the gap between regular units stats and champions.
Maybe make the regular units more attractive: more powerful / give them special abilities / allow players to keep upgrading and improve them whole game long.
Some mix might also work: make regular units cheaper and more powerful (mid late game ) and heroes less powerful and harder to come by.
Magic has little to do with why champions are so powerful compared to regular troops.
The spells i use are mostly buffs and i can cast them with 1 champion on any unit not just champions.
Damage spells are far too expensive for the dmg/utility they provide.
Debuffs are nice but also optional, I only used shrink once in a while to make sure my units were not oneshot by epic monsters.
I think some forms of magic play should be improved to make them just as attractive as buffing/debuffing.
I'd love to have a champion that can afford to spam damage spells at low lvl and win fights just as easily as a warrior or mage with buffs/debuffs.
I'd love to have an mid/end game champion that can be as efficient and successful as a warrior or debuff/buff mage .
And since I started rambling I'd like to see scary champions fighting with ranged weapons.