Kreton
Former 5x UFC Champion
The QBR thing is kind of flawed Kreton. It can go up or down at an enormous rate and every one of the qb's weapons can alter it greatly. Go look at some of the really good QBs from past time (Favre is a good example) and look at where their QBR averages out over their careers.
Completion percentage is another one people are ignoring. 63% seems to be a pretty good average and anything above is really good. I can understand the frustration with Staffords breakdowns but you cant act as if he's so off pace or any different than other QBs.
QBR is a better indication of a QB's overall play than completion percentage. Nothing is going to be perfect, but at the very least QBR factors in more than just completion percentage.
If you want an indication of whether a QB played well or not, the only answer that is correct is going to be to watch the game. But so many people want to rely on a stat sheet to determine if a player had a good game or not, and when that is the case, QBR is the best tool to use for a QB.