Define valuable.
With Ted Ginn, the 49'ers would have made the Super Bowl.
Without Santonio Holmes, the Steelers wouldn't have won their last Super Bowl.
The same as former Ohio State player Mike Vrabel. And lock down corners aren't exactly easy to find.
Plus there are a number of QBs that would be considered better than Brady. Also, it's not that hard to be an accurrate passer when all your passes are 2 step drops and dump it off to a receiver to make all the plays. Most of the yardage in his passes are YAC.