@redlantern2814: In character? Yeah, probably. Genos lets his guard down a lot, and it cost him an arm against the Sea King. If he made that mistake against All Might, he'd lose a lot more than an arm... But, for the sake of my argument, let's say they don't stop until they know the opponent is dead. Or it takes place in an open area. Then I disagree.
I'm not gonna argue for Genos' durability, as a single clean shot from All Might would end him, no doubt. The problem is, the MHA-verse seems to be rather lacking when it comes to speed feats, with its top tier, All Might, being no more than FTE. Genos should be pretty far above that, based off of his fight with Sonic later in the mango.
Sonic has been, well, supersonic since he was introduced to the show, and only got faster from there. In their fight, Genos was pressuring him really well, and even managed to cut his hair. The fact that he touched Sonic at all should mean he's well above Mach 1. (Others say he's hypersonic. I do believe he's around that level, but the feat supporting that was apparently removed.) Plus, he has energy blasts that arguably rival All Might's punches. Maybe a bit less, but definitely enough to hurt him either way.
I say, Genos wears All Might down through speed advantage and comparable DC. Though in the end, both are awesome characters from awesome series.