I think the problem is the way Oda writes. He uses a very generic forumla in his arcs in which Luffy arrives on an Island, rescues the citizens and beats up the main bad guy in almost EVERY ARC.

This also seems to be a problem with his Yonko storyline in which Luffy has to beat every Yonko to be Pirate King. In my opinion this is bad because it makes the story a little predictable and it makes the formula generic. Like, why does Luffy need to beat every Yonko? They are not all evil villains like Akainu or Rob Lucci and they have their own motivations and character.

If I was writing the story, I would have Luffy only fight One Yonko, which is Blackbeard.