Honestly, I view them as two separate issues. My opinion here [shared by many, I believe] is that the two biggest determinants of the program's success will be QB play and the performance of the OL. Nothing controversial there.
But I separate them, because I believe that the OL is positioned well to improve. We have guys coming back from injury, we have new guys who weren't available last year, and improved depth, plus a new OL coach.
As for QB -- DeVito has all of the tools, but has demonstrated a poor feel for the game and subpar in-game instincts. In shorts, he excels -- but when the pass rush is live, things seem to happen too quickly for him, negating his arm talent somewhat. Now, perhaps the competition enables him to kick it up a notch this offseason, and he'll have a better senior year than his previous seasons.
If so, great. But that's all about his growth / development. Shrader was a higher rated recruit. He's kind of the opposite of DeVito, in that he doesn't have beautiful throwing mechanics, but he's a playmaker who moves the sticks. Like Dungey, his strengths can partially mask subpar OL play, if that continues to be an issue. He started games as a true frosh in the SEC, against some very good teams, and produced [not easy for a true frosh]. He's far from perfect, but he might be just what the doctor ordered to jump start what's been an anemic offense these past two years.
So yes -- I think it comes down to whether DeVito shows improvement. If he doesn't, he might lose his starting spot.
Certainly, having improved OL play is going to benefit whoever lines up under center, as well.