A Wizard can significantly strengthen their army with mini-artifacts, and some units can be considered one level higher than they actually are. And Titans and Archmages can give anyone a run for their money – they can take out half the enemy forces before they even reach them.
As for Knights, they are simply powerful on their own. And with Griffons and their aerial attacks, they are a major headache for enemy archers. And on a large map, a Knight can turn their peasants into such a force over time that they can sweep away any Necromancer and his skeletons.