G4 Luffy already showed it had the firepower to bypass Crackers defenses as evidenced by the fact that he was plowing through the clones shields and as a result Cracker had to send them away and attack himself. His defenses aren't a problem for Luffy while he's in G4, its only a problem when he is out. It probably took him the whole 11 hours just to replenish his stamina in order to use the form again, which is why Nami's help was so crucial. You say Luffy beating Snack is baseless but Snack beating Luffy is baseless! You say Snack and Cracker should be on a similar level but Urouge and Luffy are both SN, who should also be on a similar level! So you either believe that Snack, Luffy, and Urouge are all on the same level or you believe Urouge is >>>Luffy which makes no sense. Or you believe that there is a big gap difference between Snack and Cracker.