Well, I don't know if the damage caused by Bellamy's Spring Hopper is comparable to the damage caused by Law's Gamma Knife man...
The fight with Cracker was more of a battle of stall, perfect counter for someone like WCI Luffy. Doffy could just bypass all the buiscuits soldiers, by flying and using his versatility, to hit directly Cracker's real body.
It became a battle of stall thanks to Nami, otherwise Luffy would get killed or win with a extrem extrem diff fight or even losing where he wouldn´t be able to save Sanji anymore. Nami nerfing Cracker hard was the key to beat him in the end in a stall battle, otherwise it would go into a different route, not looking good for Luffy.
flying would not help much, Luffy could fly too with Boundman, yet he didn´t overpowered Cracker defense and if Boundman can´t do that, I doubt Doffy could do it too. Only because of his versatility I give Doffy a chance to push Cracker to high diff.
In terms of defense, Ap, haki, speed and overall states Cracker is above Doffy.