Would these guys have "developed" though? The NBA isn't really looking for development, they're looking for potential.
For example, would Lydon have improved on being picked #17 by staying another year and playing out of position at the 5?
Besides all of that, it's fairly presumptuous for the OP to tell other people what they should do with their life. All of these guys had a couple years of the college experience, and maybe that was enough. Maybe it was more than enough. If a kid who goes to Newhouse can leave school after 2 years to be the play-by-play announcer for a pro team, would anyone begrudge them that?
I wish people were more honest in these discussions. For the most part, people just want SU to be better at hoops, and that means keeping these kids in school. There's nothing wrong with that perspective, but people should own it. Not pretend its about some nonsense concern about their life experience.