The few things I want to see Justin improve on have nothing to do with arm strength.
1. Ball security/less risky pitches
2. Looking off defenders/not locking onto primary receiver
3. Taking a better line on triple option runs. He loops around after pulling from the mesh and loses 1 to 2 yards that have to be regained. I still don't know if he's supposed to be doing this or not, but I don't remember any of our other qb's doing it.
1 and 2 could improve, and I think it will with time. He's only a RS-So.
I see what you're saying on #3, but it may not be as big of a deal since he's so fast. It may actually give him a bit more space to maneuver around defenders on the edge.
As for his passing, I think it's fine. The ball comes out quick and hard. The only thing that worries me a bit is how low the ball flight is sometimes. Need to get some air under it for longer passes to give the receiver time to spot the ball and setup for the catch. But remember, our offense is designed such that when we throw we should have a wide open receiver or a guy in single coverage. If we run the ball more effectively, the passing game will come together.