My opinion:
When Josh execute the play as called, protection is good, he is accurate. All of those Cole Beasley connections are evidence.
When 1st couple reads are not there, or protection breaks down (quite often until last year), Josh is into the improvise-mode and really good at getting the ball to those who flash open. This is the kind of delicate balance I don't think he has achieved: there are times that if he stays in the pocket just 1/10 of a second longer, he might have a play there, Brady, Manning are the best in those world. Buy Josh/Mahomes had so much success on the off-script plays, it's hard to find the balance. And you see teams are starting to adapt to defend that style.