You have a starting a QB who is really struggling with your base offense. The excuses are starting to wear thin. Vad saw extensive playing time last year and has played 9 games this year, so the experience excuse is running out of steam.
Ideally you may be better off going to more of a run and shoot, but the o-line can't pass block and Coach Johnson is not totally comfortable with that.
The other option is going with Justin Thomas. Thomas is clearly the better option QB. Johnson isn't Gailey stubborn when it comes to QB's. He will pull a struggling QB.
So why is he is sticking with Vad? I think there may be a couple of reasons. Thomas has telegraphed some of his passes. Also, it may be the physical difference. Vad is a solid 6-2 over 200 pounds. Thomas is generously listed at 5'11 and I doubt weighs more than 180 pounds.
The problem going forward is that the defense is not going to hold UGA and Clemson to 10 points. We'll need to score more against two defenses that have looked shaky this year. Right now, I have my doubts if Vad can put up those kind of points. If we don't, we limp home 7-5 with a 5-5 record against FBS teams.