He can throw better than most spread-option QB's, but his ability to read and adjust on the fly, when it comes to looking for WR3 and WR4 is below average, at best.
There were many times last year, that he would look for WR1 and WR2, and then take off running, right as WR3 and / or WR4 would be breaking free for a potential big gain. Either that, or he can't doesn't see when a receiver breaks from the route to become wide open.
He has made steady improvement in the last few years, to the point where he's a serviceable QB, but he's holding himself back by not learning how to be a smarter QB.
That, plus if he keeps running like this, all of the hard hits from those 250 lb, fast linebackers will turn him into an old man faster than they did to Cam Newton (who was bigger, stronger, tougher, and faster). Even those safeties making those tackles are 20 lbs heavier, and significantly faster than college safeties.
At this point in his career, he's closer to resembling the 1991 version of Steve Young, which wasn't too bad of a situation with that all-star cast around him. It wasn't until Young finally learned to stay in the pocket, look for those other receivers, and stop running so much, that he became one of the best in 1994.