I would argue that the Higgins goal line fumble cost the Browns that game. Chiefs played 1 really good game of the last 6 they played to end the season. And that was vs Bills.
Browns are absolutely legit. Chiefs reset OL but in terms of continuity the Bills and Browns are ahead on that front. Each year is different but the Browns are a contender on par w Bills. Ravens, Titans, then Chargers as dark horse.