Look, I am not defending the scheme. IMO, their players for various reasons have limited them on offense. That doesn't mean the play calling or scheme is any good. Multiple things can be true at once. But I also look at history. From 2014-2018 when he had great offensive players, Tomlin opened up to the point where on occasion I would yell at the screen to run the ball. I would fault him more for the players he assembled and some of his player choices than scheme in this regard. It's still his fault, nobody is getting left off the hook. I think he felt if he could limit mistakes on offense his defense could keep them in games. And it worked a lot, we have to be honest, until they would run up against good teams late in the year or playoffs.
As for backup and rookie qbs, I don't understand that, either. But there have been plenty of times the defense has shut those guys down, too. Players relax, figuring it will be an easier day?