Yeah, off the top of my head, the last enemy Luffy dominated was Bellamy - back in the the Jaya Arc. He had a more usual shounen struggle against Enel but since then he's been royally fucked by everyone he's taken on apart from Blueno (even Foxy went to town on him). He had to be carried away after fighting Lucci and since then has been defeated by Aokiji, various Pacifistas, Kuma, Kizaru and Sentoumaru. He only managed to scrape a win against the Boa sisters because that fight was used to show his accidental use of the King's Haki. As I said, the struggle against Enel and Foxy was more the usual sort of shounen struggle but almost every single fight against a significant foe since that point has left Luffy defeated.
(OK, so he also beat Usopp pretty easily but I'm ignoring that...)