Heroes of Might & Magic III: Horn of the Abyss

If you reason like that, then even upgraded Gremlins can be considered an imbalance, if the other player hasn't had time to upgrade them.

Perhaps, but you need to consider that level 7 units are the main army in the game, especially in the later stages.
Units increase in stats as the game progresses - after level 7, the strongest level 8 unit in Haven is twice as strong (!).