look if devil fruit powers didn't have limits, luffy would be invincible too. he would become so soft he'd just flow along the blades' movements like water around a baseball bat.
so let's just drop the 'if he could split into protons and neutrons' theory ok?
and no, mr 5 isn't going to cause a hiroshima-scale explosion, or he'd have become one of the hachibukai long ago.
all the what-ifs, defeated by one line: if they could, they would