Obviously, it is a contributing factor, but I feel he had flaws in his game before the injury. Here are some scouting reports.
I posted pretty much the same thing in May of 2016:
https://cowboyszone.com/threads/im-not-getting-the-jaylon-smith-hype.348704/
Being out of football for over a year, and recovering from an injury like this are exposing holes in his games that he had pre-injury. Some players get by on shear athletic ability, like Randy Moss, and others get by on pure will power, like Michael Irvin.
I believe Jaylon Smith has always been the most athletic person on the field at every step before entering the NFL, and as a result, his fundamentals have suffered. Not to say that he's lazy or lacking motivation, it was just overlooked.
The good news is that I think he can get back on track. I don't think the injury is hampering him all that much. I think it mainly has to due with his technique and rust. With the proper coaching, he can be a quality NFL starter.