There's a contradiction in the offense IMO. The coaches want to pound the football and use play action. However, the running scheme seems extremely limited with the reliance on the pistol and to a lesser extent not stretching teams with the jet sweep. Having a great runner at QB would make the running game much more effective.
It's also possible to set up the run with the pass. That can be accomplished with a QB like Butterfield. Spread teams out, throw the football, and open up the box for the RB. This is not what we do. So Butterfield's talent will never be maximized in the existing scheme IMO which is what happened to Herbert.
For better or worse, MC and JoMo want to run first and pass second. I don't believe we'll ever see an offense that really stretches the field in all directions with the passing game and utilizes all the skill talent on the roster. So if we're going to rely on the pistol, then having a QB that scares the D with his legs on every play is critical.