Others have already stated much of this, but...:
* King does go through some of his reads but his progression seems....off. (Slow at times, incorrect at times, bails after his primary read at times, etc.). One example is that King had a dump off to Cam Harris wide open on at least a half dozen plays but King was solely focused on the other side of the field. By the time he got his eyes back over to where Cam Harris was (if at all) he was no longer available.
* At 5'-9" he has trouble seeing over portions of the line. I think that leads him to bail on stable pockets from time to time. I also think this is why he misses an open RB who releases into the flat.
* He's simply not a good passer. Not accurate enough on shorter throws and not enough arm strength or accuracy on deep balls. And a serious lack of timing on his deep throws.
* He consistently gets the wrong read on RPO running plays. Its to the point where defenses know this and seem to overplay the running back.