As everyone knows, heros are extremely powerful characters. Adding a 3rd hero (or more!) creates another power shift.
When the next hero is introduced, I would like to see a limit of 2 active heros at any given time. Perhaps a Tavern to manage your heros, and a maximum of 2 can be awake (the other is put to sleep).
This addresses a number of issues:
1. Tactical Variability: Mix and match amongst your heros, without them completely taking over the game.
2. Upgrade Options: If one hero is upgrading, you still have the other 2 to use for raids/war.
3. Still more fire power: You just finished a raid and your king needs time to sleep? You still have 2 other heros to use. (If multiple heros are down, then maybe you use gems to get enough of them up.)

