He is simply a main character who gets the most screen time.
His entire round of his most powerful form, resulted in nothing.
It was put into the shadow of Zoro's one attack usually used for AoE...
Hit by hit, Luffy is nowhere close to Zoro, Law and Killer.
Dont confuse panel time with being better.
Imagine a boundman-long round of Zoro/Law/Killer slashes...
Kaido would be long dead by now while Luffy did nothing.