https://blogs.fangraphs.com/a-tale-of-two-pitching-staffs-in-chicago/
Longenhagen summarizes how effective the Cubs starting rotation has been, but their bullpen is garbage. It is the opposite for the Sox. Starters have been meh, while relievers have been outstanding. Longenhagen really likes Matt Foster.
Most importantly, Longenhagen likes the Sox chances of making a deep postseason run over the Cubs, due to the dominant and deep bullpen. Go Sox!