38 games started in which he played on a team with horrible offensive and defensive talent. I didn't hear anyone complaining about Justin in college, only during the draft and none of it had anything to do with his performance on the field, so I'm not sure what deficiencies you mean
As a pro, he has held on to the ball too long and taken too many sacks. This season he definitely was getting rid of the ball much quicker but still too many sacks. Considering the guy is only 24, and the quality of playmakers and coaching he has dealt with, I see no reason for anyone to assume he is a finished product and we MUST move on.
As for injuries, Jaylon is hurt every year, so is Teven. Fields injuries are a concern as well so maybe OLine that doesn't get immediately pushed back into his lap should be more of a priority, instead of a second thought.