Piggyback is pejorative.
Houck was a long reliever, last year and this. Last year Cora needed several long relievers--Houck, Whitlock, Valdez, Richards, and even Pivetta--because his starters had a tendency to struggle. In their second ALDS win last fall @ Tampa Bay, the Sox won because Pivetta pitched 4 innings in relief. Whitlock did the same thing, only it was 2 innings, to get the decisive third win. Neither pitcher got a save.
I do think Houck is the best choice for closer now--except of course, he won't be for the three game series in Toronto--but I also think long relievers can be valuable.
Indeed, I always get a little torqued when a given reliever just obliterates the opposition for one inning, maybe 12 pitches, with no one reaching base--only to see him hit the showers because one inning was/is his limit. Then the next guy comes in, doesn't have it that day or night, and gives the game away. It's as though the manager--and I'm not pinning this on Cora--is searching for the one reliever who can blow the game.
I know the paragraph above is an oversimplification and that Cora and other managers have all kinds of statistical data, which I obviously don't have, to base their decisions on.