Come on do you really think base luffy = hybrid kaido in physical strength?
To continue, we should agree on what physical strength defines.
Kaido is much faster and agile than Luffy. Also his scales, tough zoan body and regeneration makes his defence much better than Luffy.
If strength defines punching someone and make them fly, hold someone in its place, endure opponent's attacks without problem. It is not me but the manga shows that they match each other on that aspect.
In Katakuri fight, Luffy could not match Katakuri's punches, his hands got hurt and what Kata said was his armament haki is superior to Luffy's. So do we think Katakuri's base strength is levels above Luffy?
I get you, Kaido is a monster as in your nickname and well known for his power but small people can also be crazy strong in One Piece universe.