It is not that fates are bad per se, but been there done that.
They were in diadem. They were in Eureka. They were requirement to grind old relics.

Are they trulynthe only way to implement a powerful boss to fight? No.
Perhaps they are the easiest however, since code already there.

Hunts are't the same as fates. Hunts spawn in different places.

And you didn't notice I added the idea that the hunt should move around, roam the map. Maybe have it change element depending on where it is or spawns etc.