Asgard Moria was garbage. Nightmare Luffy has been Luffy's most broken form of help so far in the series.
Moria sucks but it's very likely that Luffy's own fighting ability wouldn't have been enough to defeat Thriller Bark. The great thing about that whole thing is that it's good for the story. It places a very sensible limit on Luffy's fighting powers up to that point. It made them getting wiped out not long after that even more believable! Usopp basically admitted that Luffy was carrying the crew at that point at the end of Thriller Bark too, which also worked to foreshadow the limitations of the whole crew as well.