I'm sure they can. But there's a lot more a young QB needs to learn in the NFL. That's different from any other position.
Brady was key to NE's success, but BB created NFL Brady to a large degree. And he won 6 rings surrounding him with a lot of guys he throw away and replace. Under how many HC's would Brady have become the GOAT?
I can't comment on the future of O'Brien/Mac. Wasn't my point. Sure it might work out. Or it could just be O'Brien assuming he can do it all. We know how that has worked out...
I'm sure Brady helps Josh with certain things. Intrinsically, I'm not sure how he helps him with the nuts and bolts of the mechanics of throwing, moving around and out of the pocket, etc. Not sure if he even needs to at this point. Josh is a 5th year vet.