Josh Rosen is already the third-best quarterback on the roster, at least
Ryan Griffin has been a great story to watch, but the Buccaneers have no reason to keep him on their roster any longer. If Tom Brady goes down, even Blaine Gabbert falls short of what would be needed to meet expectations, so Ryan Griffin is a far cry from what the Bucs need with his important roster spot.
At the very least, Rosen is better than Griffin, but it is worth considering that Rosen would be a better backup for Brady than the injury-prone Gabbert. Rosen has struggled in the past, but the Bucs would anyway without Brady at the helm.
Gabbert and Rosen were both drafted at 10th overall, and both went to teams with struggling offenses. Their first seasons went in similar fashions, but Gabbert was at least given the benefit of additional opportunities to prove himself.
Rosen was never given that second chance with a team, and continuously bouncing around completely dismantles any possibility of growing as a player.
Perhaps all Rosen needs is one year on one of the most potent offensive units in the NFL under Bruce Arians to see improvement, where he could become one of the best backup quarterbacks in the NFL.