I'm not sure what RBs Florida has squandered.
Going back, all I can think of is Mon Williams, who was like 6'3" and from TX, I believe. He just didn't get on the field. And the guy who was 2nd in all the FL HS rushing records, but he tore his knee up twice. Ah, that was Willie Green.
A time frame would be useful here, but oh well.
I'm bored and gonna look at it. 247 has top recruits, at least the top 247 of them (Cheeky). Here's the top backs they've gotten, which accounts for a lot of but not all the four/five-stars.
Ciatrick Fason No. 9 nationally Topped out at No. 1,267, so good
Kelvin Taylor No. 21 Topped out at 1,035, never a high end stud, but a low-end one
DeShawn Wynn No. 48 Best year was 699 yards in 14 games, was a starter on a title team
Chris Rainey No. 45 Peaked at 861 yards, but was solid every year
Mike Blakely No. 58 Quit
Willie Green No. 103 Body fell apart
Mon Williams 95 Bust, RIP
Jordan Scarlett No. 117 Ran for 889 and 776 yards around an injury, so fine
Chevon Walker 107 Bust
Bo Williams 132 Left
Mark Thompson No. 5 JUCO Two so-so years as a third stringer
Mike Gillislee No. 144 Ended career as a 1,100 yard back
Dameon Pierce No. 201 Not high usage, but effective in first two years
Nay'Quan Wright No. 261 Hardley played as a freshman
D'Anfernee McGriff No. 257 Didn't make it
Adam Lane No. 272 Helped a bit as a freshman, then left
Jeff Demps No. 257 Topped out at 745 yards, but dipped the next two years
Skyler Thornton No. 148 Mostly a bust
Markus Manson No. 214 Nothing after an OK first year
Mack Brown No. 85 A mostly bad back whose best season was not that good
So in terms of top-300 recruits, no one blossomed into a high-end star, though there were a good number of low-end stars or very solid to good backs.
Some of it also has to do with expectations. We expect more from good recruits, or high draft picks, than we should.