Agree completely. It’s a proprietary calculation based on play results vs EPA, then modified by quality of defense and time of game.
A good illustration of how useless this metric is comes from Penn States QB, Drew Allar.
In week 1, he was 22-26, 200+ yds, 1 TD, 0 Int, 0 fumbles, 20+ yds rushing. All drives led to points, his team didn’t punt once. And his team won.
His QBR was 38.3, below average, and placing him 95th of 125 QB in D1.