He isnt. His AP is pisspoor.
		
		
	 
 Lol The same AP that will no diff RS durability 
Base Kata trashed ichiji whose durability >sanji
Also Sanji isn't Luffy, Luffy survived because of his insane willpower and Katakuri personality 
AP isn't everything, it's like saying Fuji or X isn't top tier coz their AP and other stats sucks 
Katakuri is the strongest commander. Deal with it. 
The difference between Kata and Doffy is FS and G4  tier stats 
The difference between Doffy and Commanders is CoC and awakening. Onky Cracker and Ace (conqueror) can rival Doffy's and push Kata perhaps to high diff 
The difference between Kata and the rest of commanders is huge.