My issue actually is Jinbei's lack of potential due to his age. Not saying old men can't grow (Brook for example) but we can't deny that the young men (Luffy, Zoro and Sanji) have much more potential to grow. Jinbei has already lived his most of his pirate life. He's had fierce duels, he's had his name known around the world since a long time, has joined Yonkou crews (Whitebeard, Big mom) etc. Basically he's at his limit now. I don't think the fandom will like it if Jinbei suddenly becomes super strong out of nowhere and defeats an admiral in the near future. That's not the case with Luffy, Zoro and Sanji. They're growing young men who can potentially become strong enough to beat an admiral in the future.