It’s not just the oline. It’s also the coaching/game planning. So yes... he could be. The same way nobody would care about Brady now if he was the Texans first game ever starter like David Carr. Remember Brady wasn’t an amazing offensive machine or anything his first few years - he was an incredible game manager with the greatest coach ever. Give him Don Capers and the worst offensive line ever and he would have been horrible.
Bill Obrien being a OC for the Patriots proves that all the actual decision making on offense is up to Belichick.