According to Pro-Football-Reference, Drew Brees Approximate Value 8th All time among all NFL players.
Incomplete list for top 10, where is:
Eric Dickerson might have had the best speed to size ratio of any RB that has ever played in the NFL. No guy that big should have been as fast as he was.
Gale Sayers might have been the shiftiest RB, but he wasn't very big... and didn't have a long career.
Emmitt Smith was a straight ahead power runner who didn't have great size either.
Tony Dorsett could outrun everybody, but wasn't big.
Jim Brown was big but was not a speed merchant. Brown appeared to run TOWARD defenders instead of toward holes (since he was a FB he made his own holes running through defenders).
I realize this is a digression from the original subject, but the mention of Eric Dickerson got me thinking.
Walter Payton seemingly had everything, but he didn't have great size either.