Evaluation of QB
QB's are responsible for all facets of game, including catching, offensive line and performance of defense, injuries, special teams and all coaching decisions [for both teams].
The only true was to evaluate a QB is by subjective opinion. You can always find appropriate stats to support whatever opinion you already have.
Eg Tim Tebow
If you like Tebow the best metrics are W/L record and victory over Steelers in playoffs, if you don't like him use QBR or completion %age.
In rare case when the stats do not support your subjective opinion ie if you don't like QB and he has good W/L record and good passing stats he is obviously a system QB or game manager. Eg Tom Brady as Cassel and Garrapolo as both were able to win in Patriots system.
BOL
BOL