Doffy handled everything shy of Gear Fourth- he tanked Gear Second and blocked Gear Third. When Luffy went Gear Fourth he was kicking Doflamingo around the island in a one-sided beatdown. Big difference.
Luffy hammered him with Gear 4th and he still got back up and had plenty left in the tank to use his fully awakened DF powers, and should have finished Luffy off had he not been the arrogant fker he is an face Luffy's attack head on like every other idiot in the past…
Kaido is on a whole other level. I struggle to see how Luffy could even physically hurt him based on what we've been told.....