Kirk Cousins pick 4.7

[warriorzpath]

IMO, anyone determining a player's potential or even ability mainly based on past stats should be shot. I know every quarterbacks' situation is different, and really that's my point.

Here's an example of 2 nfl quarterbacks' career qb completion %. the first one's retired and the second one's still actively playing.
1) 56.9% after 16 seasons
2) 60.8% so far after 6 seasons.

The first one's John Elway and second is Jason Campbell. So tell me now, how useful are these stats (just on their own) when determining playing ability and potential?