In terms of 1 punch knockout power if 10 is highest I'd give PAC an 8. He is not as devastating as Valero, Hamed or even Juarez but because of his SPEED his 8 rate power is doubled because by the time you landed a punch on him he might already have landed 2 of his Pac power punches given that you trade with him toe to toe.
So yes they are right it is an accumulation of power punches.