What you guys need to consider about Moria's and Crocodile's losses to Luffy is that both had losses that were incredibly situational. If it was a one on one fight, I think results would be quite different.
Luffys victory over crocodile was situational? How so? It was a one on one fight in an area that crocodile should be invincible on and he got smashed. If they were to fight anywhere else luffy would be able to take down crocodile easily, see whitebeard war.