I'd argue that Roberts' return skills made him worth keeping. I didn't realize that Sherfield played mostly on STs, which would explain his paltry production as a WR, but I'd be hard-pressed to name the receiver that was let-go who would have been significantly better in the offense and also be able to play STs. And Kumerow started-off on the PS and was shuttled back and forth mostly, which is something they could do with Hollins.
Which brings me back to whether Hollins is worth enough as a STer to supplant a guy who can give you 500-600 (or more) yards at WR like Claypool or MVS, assuming Coleman, Samuel and Shakir are locks? With the understanding that they'll probably just be keeping 5 WRs like they usually do.