Didn't do. You haven't realized yet that you're making an entire argument oncspeculation and rumor. You have no evidence to support what his role was. What exactly did he do with play calling? What exactly does it mean? Did he actually call any at all? How many? Was it just situational? A million questions which you have no answers to.
This is silly.
And if you really want to know why game plans could open a little from one year to the next when the personnel wad talented and experienced enough to handle more... I mean, there's your answer. You really can't figure out why the 2019 offense moved the ball better than the previous year? And 2020 better than before that?
You can't figure out how 2020 Zach with Romney and Dax and Allgeier with a veteran OL did better than 2018 Tanner with Hifo, Collie, Shumway, a 5th string RB, and a mostly freshman OL?
Yeah, that sure looks like it all comes down to "playcalling."
Amazing how this board can simplify a complex sport down to "playcalling."