Well I haven´t seen that much above-160-million-guys in action actually.
Crocodile was really the only one on that level that showed us all he´s got. Doflamingo and Kuma have a higher bounty but we can´t actually say anything about how much they rely on DF powers or not. There really isn´t any rule that determines how physical above guys with such an high bounty have to be.
I agree. There is nothing saying how physiccaly powerful a 160 million pirate should be. It's just that when you think 160 million you think powerful. Of course it doesn't have to be physiccal power. A lot of crocs power is him being able to do what he can do with sand. I'm just saying when you hear 160 million, you think immense power.