That's prettymuch iff he doesn't catch them all in the fireball, because 1/2 damage is going to kill them.
Either one sounds like a pretty profound advantage to have over creatures you can auto-kill with 40' wide explosions.
Well, relative to 3.5, anyway.
Which kinda sucks for the whole Conan-standing-on-a-pile-of-bodies trope.
That is, the wizard archetype is supposed to defeat armies by standing on an unassailable tower or mountain peak or cloud castle or whatever and raining down spells on them - or scare them away with an illusion - if he's supposed to defeat armies at all. That still works, if you can arrange for such a spot. The archetypes represented by the fighter, OTOH, are supposed to defeat armies by scything through them like wheat and ending up standing on a rampart of their dead - again, if they're supposed to defeat armies single-handed, at all. 5e has issues with delivering on that. It's not alone, most editions of D&D had problems, either with the fighter getting killed, or the player & DM getting repetitive motion injuries from rolling so many dice trying to resolve the tedious scene.
You could always hand-wave such things, play through the first round of slicing through orcs and just 'story mode' the rest, conveniently ignoring that the PC would be beaten down in less than a minute. Or adopt some alternate mechanic, like the 'mooks' mechanic from 13A, which conveniently converts high DPR to piles of dead enemies.