Laron Landry runs a 4.38 and he has problems.
If by problems you mean he was an all SEC-safety, first round draft pick, all-rookie pro bowl alternate whose main problem has been injuries, then yes he has problems. Is he the best coverage guy, no, but he's been a starter since day one in the league.
I'm not saying Riley needs to be a safety, LB, or anything else, I trust the coaches on that. I would be thrilled if Riley turns out to be half the player Laron was.