The Mad Lad did it
Anyway, let's get to it
AfO scales to 371.558 Megatons that was performed by All Might, though keep in mind that this wasn't done casually
Kessler is immensely superior to a 347 megaton feat that was performed by Cole early in game
So they're pretty close AP wise
Since AfO knows about Kessler's powers, he's gonna know to stay away from his clones and try his best to play keep away and try his best to tire him out..
But since Kessler knows that AfO is a pretty powerful guy, he's not gonna play around either (he doesn't in character anyway). He's gonna stick to his usual MO, spam clones, spam summons, all while using his TK to keep AfO where he wants him, and use his ranged attacks from afar
Now, AfO has an answer to clones and summons. He can use his air blasts to destroy them from afar. His infrared sense and other super senses can help with the invisibility aspect of the drones, and will never let Kessler slip under his radar
But Kessler has the answer to a lot of AfO's ability, despite prior knowledge. His passive barrier will keep AfO's tentacles from touching him, which means no power steal. He could also surround himself in lightning to serve as a form of pseudo armor. His radar sense can keep track of teleports like Sasha and Nix, so he doesn't have to worry about AfO's teleportation catching him off guard. His Regenerationn will also help him stay in the game longer.
However, AfO still has no answer to Kessler rag dolling him with his TK, and Kessler has the advantage in ranged attacks (lighting bolt, beams, shockwaves and grenades >>> air blasts and bone drills)
BUT, this is Prime AfO, who has an unknown amount of Quirks at his disposal, so who knows what he has up his sleeve.
Though, Kessler was also implied to have some abilities hidden away when he came back to the past, but that's beside the point. Also, paradoxing, but I'm gonna assume that's restricted for now.
Going inconclusive atm due to both having counters to each others powers and cause of AfO's hidden abilities
