My main concern with Alex comes from what
@aceboon mentioned above. He's not quick enough to defend 1s or 2s. Many NBA 3s would blow by him but there are enough less athletic shooters in the league that he can get by. Then there's 4s, where he gives up a lot of size and athleticism to many of them. You like him on LeBron? Giannis? Banchero? Mobley?
I don't see any position where he'd be an average or better NBA defender. So his offense would need to be really special. I truly hope he has a long, successful career, but I wouldn't be surprised if most of it is in Europe, where I think his game fits better.