Akainu resisted the attacks of the strongest man and pirate in the world who also possessed the power to destroy the world 3 official things that Luffy does not possess.
Akainu possesses stamina, defense and durability feats that make him superior to anything Luffy has faced so far and not to say that Luffy's gear 5 doesn't last long.
Akainu mid diff to high diff by far just because of the toon force 💩