Boros in his strongest form starts breathing heavily and is commenting on how taxing his form is after just one punch and a kick.
He starts trying to go past his limits to continue to enjoy the fight, but gets one shot, so he decides to end the entire planet because he knows he has to use everything to win or he’ll lose to stamina. This is like less than 3 minutes of actual fighting that he can be in his peak form.
The only problem that exists is someone stopping the Planet Wipe attack.
Todoroki could freeze him before he pulls it off I suppose, or negate all the heat build up since it seems to do its damage via high heat.
Deku could also wait until the exact moment he is going to fire and just use higher LS to make him shoot in a way that doesn’t hit the earth via Gear Shift blitz.
Also since Deku is in 45%, he won’t start with Gear Shift. He’ll just fight normally and with Fa Jin boosts while dodging. Bakugo and Shoto are gonna be the actual showrunners since Boros doesn’t have the heat resistance to not get incinerated by their attacks. So if anything, they’ll be the ones overtaxing his regen by just blasting him over and over, and Todoroki especially can beat him down by freezing him solid + Flashfire Fist incineration.
Deku will likely use Gear Shift when Boros starts wanting to go crazy and end the planet, but he would have to either Fa Jin drop kick him out of charging the CSRC, yank Todoroki with him to freeze Boros, or just redirect it a tiny instant before it fires to make it miss the planet.
They have options to win, it’s just funky.
Deku is the only one that can do real damage straight up with force through Fa Jin, so the only “one shots” going on are through incineration. Everything else kinda bounces off Boros from the stat gap.