there are exceptions and outliers to every rule.
no one single statistic completely defines a player.
total QBR is an excellant tool. it's passer rating on steroids, giving credit or factoring in a qb's actual contribution to a play. avoiding sacks, get running yards, clutch time vs garbage time, intentional grounding, fumbles, scrambling, dropped catches, yards after catch, pass interference penalties, down, distance and much more.