We're seeing this offense falling into place a piece at a time IMO.
GRob was a huge addition. With him and Roger on the interior the OL is a big mismatch on any given play with even a DL like Seattle's. They're gonna make holes on just about anyone IMO. They now have 3/5 playoff level OL at LG/RG/RT and will keep getting better as they go.
Also, it is possible that Jake Long will improve as well, since he is coming off that injury. If that happens this OL could gel into one of the better units in the league. The talent is there.
Mason changes things too. His burst suits this OL very well, and behind him there is playoff level depth. I've said all along that Fish loves to have his horse, and no matter what he says he has finally found it in Mason. Stacy just can't do it with his injury tendencies, sadly, but with Mason you get big play ability that is a very, very nice fit for this team.