The issue is that his team has repeatedly said they don't want him gaining weight tho.
I think his shot is the least of his issues. His rebounding seemed weirdly not great, his height was a hindrance to his handles, and his motor was off, along with conditioning.
Now these can all be fixed eventually, but we say the same chit about all the big men and for a lot of them it never materializes
His shot has always been pretty below average from 3 and the parts of his game that had people drooling was the thinking his shot was KD and he can handle the rock like a wing.
He's 7'4" and 210lbs, he has to gain weight even just through natural body maturity (yeah, Manute Bol begs to differ but even Bol Bol is 220lbs and he's shorter than Wemby). KD is the "Slim Reaper" and he's at least 25-30lbs heavier at over four inches shorter. I have a hard time believing that Wemby is gonna play at anything less than 230lbs, and he'll be faster at that weight than he is now too.
What you say about his height being a hinderance to his handles is one of the main reasons that I feel the hype on him was overblown. If you're 7'4" then you can surprise guys and make plays with your handles, but that's never going to be how you dominate. At best, it's a nice counter that keeps the defense honest. For him to become a great player at 7'4", what he has to be great at is defense, rebounding, shooting over defenders, finishing, and court vision. Do those at an elite level and the sky is the limit. Ballhandling is a supplemental skill, it's not the game.
Now, does Wemby have the defense and shooting and vision to become a GOAT? Clearly not yet. But you also can't say that he won't have those things. And that's why his ceiling is so high.