I imagine that the coaching staff has already evaluated his skills as it relates to a returner, and if they were that good, he’d be on returns. If you’re fast, but have stone hands or make undisciplined decisions on the field, a coach isn’t going to risk putting him back there. He’s already a DB, which implies that he doesn’t have as good of hands as a typical WR or some RBs. I’m sure Holtz evaluated players similarly, but probably just happened to have a couple players who had the speed plus the other skills needed to be effective returners.