One thing I will say I like is that the Dolphins recognized fairly quickly that Rosen was lacking in intangibles (leadership, attitude, etc), and pulled him until he can correct them. Is that something he can do? Hard to say.
What I will say is this: Anyone who says "Josh Rosen is a waste of time, kick him to the curb" isn't paying attention to something very specific. Josh Rosen is two months younger than Joe Burrow. And he's been in the NFL for two years. So he was hardly a finished product when he came out.
It costs the Dolphins absolutely nothing to keep him on the roster. They have him under team control for peanuts for the next two years. Let the team work with him on his flaws, because he's got all the tools to be a very good QB. If all that ever comes of him is that he's a good backup, there could be worse things. Ask the Eagles how important a backup QB was when they had to go to Josh McCown last weekend.