True but Cracker used his real sword to cut Luffy's arm. Bellamy's own hardening + attack power overpowered Luffy's hardening whilst Luffy only used invisible Haki against Hody's bite, didn't he?
Well, Doffy used his Flap Threads - an awakening attack with hardening. This spamming attack was so strong, it crashed him into a mountain and made a hole on said mountain. This attack was clearly one of his strongest.