Gammadoodler
Hero
The point was what level of enemy density is required for caster aoe spells to 'catch up' to high level martial damage with supporting feats and magic items.Is the party fighting 4 Solars? 4 ancient dragons? 4 Balors? 4 Pit fiends? 4 Liches? If the party is fighting 4(or more) of a CR 20+ encounter, they're probably all dead before the fight begins.
That fireball is going to be less than stellar against most fights at that level.
For a level 3 fireball, available at caster level 5.. 4 targets.
There was no intent to debate the tactical merit of fireball in particular in high level scenarios, and I rather suspect that high level encounters will have some variety between single or a small number of individually high threat targets, and larger numbers of individually lower threat targets that are dangerous due to their numbers.
The general point is that where there are more enemies, caster damage gets waayy more competitive with and can exceed martial damage (and its not the only thing the caster can do).