Fields was not known for holding the ball too long in college. His scouting reports did ding him for slow operation, but that's not the same thing.
Actually, go look at the weaknesses on fields' pre-draft scouting reports, it's uncanny how accurate they are to what his problems have been in the pros:
https://www.nfl.com/prospects/justin-fields/32004649-4576-9504-963d-c33127e80752
Fields, however, did have superlative college results his senior year. Like you said, we need to look past numbers when looking at college QBs. College results do not tell you anything about how a QB is going to play in the NFL.
A college qb who did have a reputation for holding the ball too long had this under his weaknesses pre-draft:
"Too eager to go big game hunting Ravenous appetite for the explosive play can also bring unwanted trouble"
His name was Patrick Mahomes and he turned out alright.
Diva? Meh, most elite athletes are. As long as he channels it into work ethic, which by all reports he has, I don't care.
The only legit criticism here is his height. He's not Bryce Young levels of short but it would be nice if he were a smidge taller. He's taller than Russ Wilson or Drew Brees, so I don't think it's disqualifying. He's an inch shorter than Aaron Rodgers.
But he does have a tendency to think he can stand up through hits and shrug them off, and he's nowhere near big enough to do that against NFL defensive lineman, so he will need to remove that from his habits.
This isn't even the first time this thread has been posted on the last 24 hours