Ofcourse its an incredible feat. Still a feat that no one else can replicate its exclusive to Jozu. That doesn't mean Jozu is unbreakable. Essentially Jozu is a better version of Daz Bonez. He is a swordsmans weakness just like Daz was (except now you need to be able to cut diamond instead of steel to overcome him which is in GOAT territory). Using a cutting attack to measure his defense isn't the best method. Luffy will be able to hurt him plenty in G4. He nearly changed the entire topogrophy of Dressrosa, heavily doubt he has trouble hurting Jozu.
Using feats here and there from the war also aren't saying much. Its like me saying
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tanked a named attack (similar attack as the one Aokiji got hit with) from his so what makes you think he can put Luffy down?
But obviously I won't use that, I'll just use power scaling to tell me Jozu isn't far off from Doflamingo.