IMO, guys reach their max, if they work. Higher rated guys may have maxed out already or didn’t work at SU. Not sure who left SU and starred elsewhere. Lots of top ranked guys fizzle out at Duke, UNC, etc.
Personally, I don't think it is that black and white.
Historically, JB identified lots of darkhorse guys who ended up being really, really good. And every program has recruits who don't pan out, so I don't view that as an indictment on JB.
BUT that said, we've had an inordinate number of "misses" post-sanctions that have really hurt the team. And the impact of those misses has been exacerbated by lack of depth due to reduced scholarships, and due to missing out on some of our key targets [Quade Green, Thomas Bryant, etc.], and due to unexpected departures from key players [Ennis, Lydon, Mali, etc.].
Specifically, Kaleb Joseph was the hand-picked successor for Ennis. If he'd been capable, he would have stabilized the PG position post-Ennis. There's no shame in a frosh not being fully ready, but where was the development heading into year 2? And then a few years later, the hand picked guy was Carey. Meanwhile, both of those seasons we passed on OTHER guards who might have helped a helluva lot more.
We also have examples like BJ Johnson, who didn't develop into a contributor here but ended up proving to be an NBA caliber player after leaving. Why wasn't a physically underdeveloped kid like this redshirted to give him a year for his physical maturity to catch up with his athleticism, and maximize his development long-term?
So while some of it may have to do with work ethic, that doesn't tell the full story. I think some of the inconsistencies with respect to player development may have to do with the staff, JB's waning involvement over the past few years [especially before the Hopkins departure], and recruiting problems.
We've had highly rated players excel and outshoot their HS rankings. CJ was injured coming out of HS, so his rating was probably too low -- and he became an All-American. Gbinije [from your example] was a McD's AA -- he just needed a change of scenery to get on the floor. Grant was pretty highly rated, and had outstanding bloodlines -- but he didn't show any semblance of the perimeter skills he's shown at the professional level while he was here;
his development seemed to take place AFTER he left SU.
But in the main, player development has been a problem area for us for an extended period of years. I don't think that there is any one "root cause," but I can't overlook that when I see statements like you made earlier about JB's player development being "unparalleled" -- that overlooks a lot of significant evidence to the contrary.