I feel comfortable ruling out weight loss as a key factor in THT's shooting and decision making development as well as the players you mentioned, but to each their own.
Getting in better shape makes you a better basketball player. It's a very different thing from skill development for me. Never have I ever saw a player that sucked at shooting and thought....man he really needs to lose weight and that will fix it. IMO, THT is a classic case of a good athlete with low skill ability. It's not a bad thing to go from good to great as an athlete, of course, but if a player desperately needs to improve his shooting and/or decision making his weight is one of the last things I will think about in terms of that development. If a guy can't shoot, his weight is one of the last things I would find myself blaming it on. This is especially the case for a guy like THT who desperately needs to be able to make wide open stand still jumpers. Someone like Keyonte is a different story, where he needs to be able to create more separation because the defense is breathing down his neck when he's shooting. But even in Keyonte's case, I wouldn't say he became a better shooter I'd just say he's a better athlete.