The Cleveland Browns are living breathing proof that if you have a rock solid o-line you can have an old washed up garbage QB with no legit WR's and TE on the roster and a bunch of nobody RB's and still produce and have a capable offense. Last 2 weeks the Browns have the most yards and points in the entire NFL. Playing on the road vs SD and Baltimore, two teams that aren't pushovers. The Browns o-line is maybe the best in the league and amazing, and it carry's that team week in and week out. Makes marginal players look better than they are.
If you can protect your QB....almost any QB....in this league with the ways the rules are set up to enhance the passing game and be slanted towards the passing game, you will have success. The Browns protect McCown and even with a WR unit of nobody's, I mean utter nobody's....they get yards and points!
Look at the terrible o-line's in the league, the 4 worst this year are......Seattle, Denver, Miami, Detroit....all four teams this year struggle to do anything on offense and move the ball due to the o-line's being so friggin bad.
I've always said if I was a GM I would pay for the best Oline and Dline in the NFL. I think if you have both of those you're going to be good regardless of who you have in other areas. That might not win you a Superbowl but you'll be a good competitive team.