I actually think the secondary will be the strength of the defense next year. Holmes/Carson are both high level ACC players, particularly as upperclassmen. Greer is as well if he can stay healthy. And Mustapha, Andersen, Slocum, Roberts, and any new additions should be sufficient depth there.
My biggest worry on the defense is who steps into Fox's role and who steps into Masterson's role. DJ Taylor and Chase Jones are both decent players, but neither seems to have potential to be a high level ACC starter. I'd love it if a younger LB like Dylan Hazen, Quincy Bryant or Jaylen Hudson could make a leap forward and be the other starter with Smenda next year.