We kinda overlooked it since Jake Coker lead us to the promised land in '15, but I do remember the struggle then.
The common denominator, at least on the surface, is arm talent at qb. More specifically the ability to quickly and accurately, deliver a pass (often in tight coverage) to a receiver beyond the sticks.
Jalen struggles with accuracy and a quick release and, although JC was a little more accurate, he suffered from a very slow windup and release too.
Admittedly, our current offensive playcalling is part of the problem right now, but going back to 15 that was when Kiffen was still in control and doing an excellent job.