My impression is that Phil really likes Harris ... so I'd look for him to be an eventual "riser" for the Hawks. Furthermore, Roberts is a guy who has been climbing the proverbial ladder for the Hawks ... and has been continuing to earn Phil's trust. So I believe that the Hawks current depth at CB is a little better than the picture you're painting.
However, with that said, it is true that Phil tends to bring DBs into the program in "batches" ... and, from there, he separates the wheat for the chaff. Despite Phil being a pretty well-loved coach from "his guys" ... we still tend to have a pretty high attrition rate at DB. As we've been coming to learn ... maybe part of that has been attributable to Doyle. However, Phil is still known to be quite the yeller and is a VERY detail-oriented guy. Many players might have the raw skills ... but if they cannot learn the nuances ... they're not going to earn Phil's trust and they won't see the field as much.
Consequently, with the departure of DJ Johnson ... I kinda agree. Furthermore, we have to remember that Gulley didn't make it academically - so he failed to enter the program with the rest of the '20 recruiting class. So he's another CB-type who's not there supplying future depth for us at DB. Thus, with those losses, I CAN see the Hawks potentially looking to add another CB/DB-type.