Luffy’s punch didn’t change him. Think about it:
1. Luffy punches Alvida
Luffy punches Alvida: Alvida loses like 400 pounds, becomes drop dead gorgeous, obtains one of the most OP Paradise devil fruits and joins the crew of one of the Seven Warlords
2. Luffy punches Buggy-Buggy:
Luffy punches Buggy-Buggy becomes one of the Seven Warlords in less than a year with some of the strongest inmates from Impel Down in his crew, and creates a booming company that sees staggering success.
3. Luffy punches Wapol
Luffy punches Wapol: Wapol becomes one of the richest men in the world and makes his own kingdom, also marries Miss Universe
4. Luffy punches Bellamy
Luffy punches Bellamy: Completely changes his ways to become a respectable man, becomes way stronger, gets haki before over half of Luffy’s crew, befriends the future Pirate King
5. Luffy punches Crocodile
Luffy punches Crocodile: Oda makes him look like a badass during Impel Down and the Marineford War, gets respect from a bunch of people, and is apparently thriving in the New World
6. Luffy punches Lucci
Luffy punches Lucci: Guy goes from being a lackey of CP9 to being seemingly in charge of CP0, the strongest Cipher Pol agency.
7. Luffy punches Coby
Luffy punches Coby: Dude goes from a nobody Marine to a famous Marine Captain and is hailed as a hero
8. Luffy punched Charloss
Seriously, the only enemies that Luffy defeated that you can’t say improved are the ones who haven’t been shown again yet in the manga. There are probably a ton of other examples, but look at what happened this time. Luffy punched Charloss, probably with more intensity than any other antagonist, and the guy is exactly the same as he was two years ago. Really goes to show how obstinate and arrogant the Celestial Dragons are, and gives more props to Otohime for actually being able to change a very stereotypical one.