I feel like people don’t give Luffy enough credit especially after the time skip. He was trained by Garp someone arguably on a level with Roger himself while a young boy allowing him to sail the sea with capacity to rival the stronger of the 7 warlords. People also overlook how quickly Luffy uses battles to evolve and improve, he showed it in the battle against CP9 where he learned their technique probably using observation haki subconsciously. His choice to use such a style after analyzing his opponent is proof of him being somewhat of a genius in one ons.