Completion % doesn't tell the whole story or even much of the story. Brees has the 57 completion percentage to Rodgers 45 yet Rodgers passer rating in those situations is 86 while Brees is 61. Even that is hard to go by though because it also matters how fast the pressure got there and what kind of routes the WRs were running. If a QB gets pressured but he has a few different receivers out there close to the line of scrimmage it's going to be easier for him to get a completion than a QB who has most of his receivers running downfield.