Shaq did let his weight derail his career. He spent the better part of a decade on the pine more than on the court and his impact dropped off rapidly after his first year in Miami, largely because his weight wouldn't stop getting out of control and it exacerbated his lower body injuries. You specified early in the career, which is why you're technically correct, but if you're just talking about weight derailing a career, Shaq is pretty much one of the posterboys. How many times has he, and others, said that he could have been the GOAT if he had kept in shape? It's a frequent talking point about Shaq.
With regards Barkley, you are correct but only because - as Barkley himself has said - Malone was a tough, grizzled vet who wouldn't accept anything less and immediately took a firm leadership role and personally took responsibility for whipping Barkley into shape. Where has that kind of leadership been on our team for the first three years of Zion's career? Was it one of the rotating cast of coaches we've had, or did JJ do it in between recording his podcasts and whining?