I don't necessarily agree that standing above others and strength are what makes one a conqueror when we have characters like Yamato, Ace and Katakuri who don't possess those types of ambitions. Sanji is chivalrous to a fault, very protective of those close to him, he wants to be strong for their sake, when looking at the position he occupies, top tier strength is a must. Again, when you combine all of the points we've made, you can see a justification for him possessing it.