Everything about heroes.

A Warlock is very strong on small maps, but if the game drags on, chaos and summoning become less effective. I agree about the Elf. Here, you can choose either light or chaos. Chaos will be useful at the beginning. With huge armies, mass spellcasting will compensate for the lack of attack power, and mass haste is always useful. Not to mention the rain of arrows with Divine Retribution (at the beginning, it's worth using it on not very valuable units). Regarding the Wizard. Special Ability (SA) is very strong, but a mentor is needed, because initially focusing on SA and not developing any magic is extremely risky. Or, you need a map with the possibility of leveling up to 27-30. What works well in a campaign doesn't always pay off in other battles.