For one, I can think of many QBs that are better than either Grossman or Hasslebeck. I think you name Hasslebeck based on past success. I like WR and RB stats because they are unit based, you have receptions, carries, and yards. QBs I look at YPA but I also look at interceptions, TDs, so there isn't one stat I look at. QB Rating isn't unit based so I don't pay much attention to it.
I see about 16-17 QBs who are solid. I look at whose over 7 and also how many interceptions they have thrown. Grossman and Palmer(though he is doing a great job of getting the ball down-field) have more INTs than TDs. Rivers has 19 but I would still put him in elite category considering recent success and his ability to get the ball downfield. I'd take often injured Kolb over Orton, Hasslebeck, and Grossman.
http://espn.go.com/nfl/statistics/player/_/stat/passing/sort/yardsPerPassAttempt
Also Roethlisberger was a terrific college QB, I really enjoyed watching him play and he was touted as being in the same class as the other 2 QBs chosen high in that draft, Manning & Rivers. McCoy wasn't highly touted going into the draft. You do have a point with Brady.