This list of players is more a testament for their work ethic and desire to improve than it is for DX or NBA scouts inability to evaluate talent and current level of skill.
Totally agree. That's my point. It wasn't to knock GMs or DX or even nbadraft.
And I mostly agree with your larger point. It's not that "potential" or "upside" is a useless concept, it's just that it's more complicated than it's often taken to be. Players generally regarded as having little upside can and occasionally do prove everyone totally wrong.
What I may disagree with slightly is that the examples I chose are too much of outliers to establish the point I was trying to make. That's a healthy percentage of the top 40 NBA players in the league (by a certain metric) who were not regarded as high upside prospects.