Did you even read? Switching personalities is a separate ability than cutting. Haki protects you from the cutting power, we don't know if it can protect you from the personality switching.Enough Haki can prevent Law's attack from cutting you, Im pretty sure someone like Prime Sengoku has enough Haki to do that. Did you just say Law+2 toddlers>Gol D. Roger?
And pay attention to what I said, I said it's possible for there to be a scenario where Law and two toddlers can beat Roger by Law switching Roger's personality with one of the toddlers. I never said that's how it's gonna happen 100% of the time, or that it's likely, I said it's possible. There's also the possibility that Roger can release a massive wave of Haoshoku that'll knock Law out, or can move with enough speed to hit Law and decapitate him with one blow before he can.