Luffy should have had already been defeated by BM at the end of WCI, that really shamed BM while showing there were really no tension since a YC3 lvl Luffy with half crew (no Zoro) just step in a yonko HQ, stole her most precious treasure (road poneglyph), stayed back specifically to fight her strongest crew member (exactly what Ace did with Akainu, it is just that Sce was not the main character), beat him (aling with her YC3 previously) and have BM clown herself as the biggest obstacle for her own crew. But since it is way better for the mangaka to use the usual formula instead of taking a risk (what happened at the end of Sabaody part 1) this is what we get. After that point there was already, basically, no hope anymore.