But that's only because you say so xD
If Luffy defeats all his rivals needing help, food, protection, in several rounds, etc. So, he is simply not the strongest, because he wins with the help of others, with breaks and being protected, while his rival exhausts his resistances, continues accumulating damage and continues being bothered by others.
Against Kaido, Luffy was defeated 3 times, he was protected by Zoro on 3 occasions, he was rescued and fed by Law's crew, while Yamato continued damaging and tiring a Kaido who already had some damage from Zoro and Law, until after that, Luffy obtains the ADVcoc PU, and in the 1v1 against a Kaido already at 60% LOSE AGAIN, this time being saved and cured 100% by the god Nika, for this time yes, defeating a Kaido who was at 30%
Against the gorousei, he receives damage from Saturn, and he cannot do anything, against Jupeter, he is swallowed by the worm, and is saved (again) by the giants, he flees from Topman and needs help to send Mars flying, help from Sanji IF, Franky and Nika Booney lol
When you understand that someone who constantly needs help + being in their most powerful form, and even with all that, continues to run away, needs food and needs to be protected, is not a top tier nor will they be the most powerful, we already know who it is reserved for .