Idk, I think first we either have to prove A. He's able to hold G4 longer or B. His burnout time following G4 has decreased.
I don't think A. has been shown but I think a case could be made about B. The cracker fight we credit the sustained G4 to the biscuits he was eating and that's fine but this fight against Kata he's used G4 and ran out of G4 but he wasn't left motionless like he was against Doffy(or at least not that I remember)
Plus Luffy made a point to mention he was hungry during this fight whereas the Doffy fight he had eaten slightly prior. So idk, I think if we could prove 1 or the other than a strong case could be made that Luffy is>Doffy but idk if we can prove either of those yet.