But note that's because Fireball is, by design, overpowered. It's intentional and acknowledged as such by the designers. If you do it to non-OP spells it gets a bit less cool. But it's an interesting concept.the lowering the spell slot intrigues me
I think if you 'down cast' fireball down to a 2nd level spell cut the AoE down and lower the damage 2d it would STILL be good.