I think it has far more to do with Heinicke being much, MUCH better at keeping plays alive with his legs and pocket manipulation. That usually gives receivers/TEs/RBs a little more time to adjust and get open. So on 3rd and long, Heinicke is bouncing around back there, dipping into the pocket and then back out again, bailing a bit left and right and making LBs think he might take off, which gives his players the opportunity to get themselves open. With Wentz, that extra time rarely happened.