I think a lot of this intel is flawed.
Chase Sylvie never started at OU that I recall. I don't think he even played last year. Justin Broiles proved in the playoff that he can't cover 1on1 at all. Moving him to CB might as well be moving him to Alaska. Like many of the OU defenders already in the portal, if these guys leave, I don't know how much of a loss it is.
The Sooners will have Tre Brown at one corner. Jaden Davis, Tre Norwood, and the freshmen will be in the mix.
For the safety spots, OU has a higher floor. Turner-Yell played better in the latter half the year. I don't know if he has the athleticism to hang with elite pass catchers, but he's a good tackler and not the worst cover safety OU's rolled out. Patrick Turner set a floor for the other safety spot. He is in position and assignment sound. He definitely isn't a plus athlete, but he won't get OU beat against most teams either.
The nickel is a trash fire. Bookie Radley-Hiles did a few things well like attacking bubble screens and playing reasonable zone coverage. His lack of discipline, size, and speed mean he can't perform some basic functions such as getting off blocks at all or covering bigger or faster receivers 1on1.
OU has several intriguing athletes for these three spots (safety and nickel) in the pipeline. They defensive coaches stated that they want to rotate players at all positions, and hopefully some of the guys listed below will contribute in 2020.
Unlike Broiles, against LSU, Woodi Washington was in position and tackled effectively. The Tigers just made plays, and he did get beat then. From what I saw, he needs more run at NB, S, or somewhere. Criddell and Morris look the part and really need opportunities. Morris is apparently a bright guy too, so I don't know what's holding him back.
Some of the incoming players may hold promise for next too. Justin Harrington looks like a plus athlete, but he's a JUCO...who was supposed to be at OU this semester...and is delayed until the Summer (eye roll). As EEs, Bryson Washington and DJ Graham are apparently impressive, but what will that mean in the Fall?