There have been a couple of great podcasts/articles about why NFL teams are still so bad at picking QBs. Coupla thoughts.

1. QB is one of the most contingent jobs in sports. He can't pass to himself, or block for himself. Success is determined by forces outside his control.

2. The reverse order draft (typically) guarantees the best college QBs go to the worst teams—a situation unlike any non-sports career—which means college talent is often "rewarded" with an awful professional home.

3. Greatness is (often) non-linear. Manning was a turnover machine who quickly learned historic efficiency. Brees was inconsistent before NOLA. Brady was a super-clutch player who got better and better thru his 20s until became a statistical monster in his 30s.

If QB greatness is both contextual and non-linear, scouting will always be extremely incomplete. It's like forecasting how a plant is going to grow by doing a full genomic breakdown of a seed, but having no idea what climate or soil it's going to be planted in.