It is true it did more to prove you can't just simply fill your bullpen with retreads and pitchers who failed to make the rotation. You do need good pitchers in the bullpenand as many as possible. These guys are going to pitch close to 40% of the IP over the season.
Closers were popular among managers because they reduced doubt and made for easy press conferences, and popular with GMs because they were relatively cheap compared to starters. But last off-season, Wade Davis signed a contract worth almost 80% annually of what Darvish and Arrieta were making. The dedicated closer is moving rapidly into luxury, and it never really was a necessity.
Ideally, I'd rather see a "high leverage" guy who comes in and puts out a key fire in the seventh and eighth. However, if that specialty ever caught on, it too would become very overpriced. But over the course of a season it should lead to more wins. To me, there is nothing sillier than watching the lesser arms struggle with the top and/or heart of the order in the seventh and eighth innings, hoping they can get through so the Sox can get to the closer. I'd rather see him in there when i find myself hoping on the setup guys too much...