It's less "doom and gloom" and more being realistic. There's a reason why all big men in the league have been cutting down over recent years to keep in tune with the pace and space game. Of course, no body type is immune to injury, but all the actions that are frequent in today's game, and the injury risk they carry are compounded by the weight you carry, especially when knee injuries are more prevalent than ever, and that joint/ligaments bear the majority of your body's weight. Since "coli doctors" don't know what they're talking about, perhaps you'll find advice from NBA trainers/coaches more palatable:
"Mahinmi was given the all-clear to slim down in July, but started with lighter weights to take it easy on his knees. Losing weight also reduced the extra physical stress on his ligaments and joints when he ran, jumped, or landed.
“Someone like Nurkic—if he stays at a good weight, and he’s not fluctuating, he could add four, five years to his career,” Barto says. “He’s already had one injury,” he says, referring to the Blazers center’s broken right leg last March, “and the more weight you hold, the more you're banging your joints, and the more injury prone you're going to be.”
Players are now looking for ways to help them last—not just over the long haul of their career but over the course of a grueling 82-game season.
On Zion -
Finally, we touched base with an NBA assistant coach, who spoke off the record because he is not authorized to speak publicly on the matter.
"If you're playing 82 games at that weight, running up and down the floor, that's bad for his joints and it'll take a toll on him. I think he's going to struggle with a lot of things. If it were me, I wouldn't play over 260-to-265 pounds if I was 6-foot-7. In today's game, with every team getting out in transition, with more possessions than ever before, it's concerning if a guy is carrying that much weight.""