Zardnaar
Legend
Funny thing:
A fireball alone is not fantastic. But having 5 casters starting with fireball has a significant chance of ending a fight before it really begins.
Lets assume 3 go through. 2 are saved against. That is 32d6 damage (average 112) right away.
Enough to really soften up the opposition quite heavily.
I still think you are correct. The game is better if casters and non casters synergize. And in that case, starting out with fireball is not the best option often enough. But if you are an evoker or sorcerer, you can finish an encounter with fireball very well.
Or a controller uses 1 spell and martial mops up

5 spells to kill CR1-4 CR5+ might survive that.