R1: Okay, do we must assume all the abilities of stands. Giorno with his "time acceleration" punch on Bucciarati and "if you hit something i made alive, the hit will return to you" are broken, Fugo with Purple Haze will kill almost everyone besides maybe Luffy, Caesar and Magellan. Mista and Narancia can be a great help towards non-durability based characters. Risotto with invisibilty and his broken iron taking technique will kill anyone. If you under Illuso's Mirror World, you dead. Notorious B.I.G is unkillable. Green Day is broken. And should i say something about Diavolo and other Passione members? Or that stand are untouchable and invisible to non-stand users, or that stands are going from Relativistic to FTL to Irrelevant speed? Yes, they lack DC, but with their hax, if playing right, Giorno can become PK.
R2: Requiem solos the whole One Piece world together.