I went with Play Calling, but I'll freely admit that my frustration with Turner likely drives that. I think you could very easily make a case for any of those things.
One place I think Play Calling was such a detriment, is because we KNEW our deficiencies elsewhere, and the play calling is the 'fastest' way to work around that. At times, he was actively play calling AGAINST what strengths we did have on the team. We knew we had a deficient arm behind center, yet we had a higher Yards per Attempt, as well as AIR yards per attempt with Heinicke, than we did with Wentz. I keep going back to it, but it encapsulates my frustration perfect... 4th and 1, and you pitch the ball 6 yards behind the LOS to your 4th string QB. The frequency we run a spread offense, empty backfield, shotgun formation which forces 5 down lineman to protect the LOS while we KNOW we have struggles on the O-line. While the team is winning, we run a max protect, heavy blocking package with sometimes 3 TEs AND an RB in to at least chip defenders... then we get away from that offense over the final 6 weeks of the season when we're making a playoff push....
Wentz can't just get 'more' awareness like it's Madden. The O-line won't just 'click' and be able to block Joey Bosa 1 on 1...