What you described him doing in summer league was what Dorsey struggled to do last year. If Dorsey can play overseas in Europen, then Williams can surely play in China.
I doubt Williams can play in a top tier Euroleague team like Dorsey . You can say whatever you want about Dorsey but he is much more athletic and better defender than Williams. European teams search for undersized athletic american Centers, they don't care about their post skills because they are not going to run the offense through them. China is different.
Interesting that more and more choose china over europe. But in europe you can get your skills develop if you are a young player and go to a small team. Not in china.
I don't think you can really get your understanding of the NBA or your physical development taken care of outside the NBA unless you get a personal trainer on the side, but even then European and Chinese training standards are so idiotically unnecessarily tiresome that you won't have that much time on your own to improve. OTOH, some people need to secure a lump sum of money RIGHT NOW more than they need a non guaranteed NBA deal RIGHT NOW so it makes a lot of sense, especially for younger players if they are coming out of less wealthy homes. If he takes a quarter of his money and invests it in an experienced NBA personal coach, then he'll have the best of both worlds.