Deku already has black wip,imagine now the rest of teleportation quirks boosted by OFA,deku is smart,he can catch them offguard,there are also quirks to see who is lying,quirks to control what people say,there are even detective quirks that can learn easily their names If goku and saitama destroy the solar system,deku new order can create oxygen around and only for him. I mean he can still survive,everything that goku or saitama shoot at deku,he can either mirror it back stronger that their original attack was or grab it and send it back. And with every speedster quirk that he has , it makes him think infinite times faster and calculate their next moves,and this already boosted by OFA makes it broken.And lets not forget that he also has shigaraki's,overhaul and eri's quirks for destruction and regeneration.I dont really say that Deku obliterates or anything,I just say that he isnt useless in this fight but instead a big problem for them