While Flawed, The Red Sox Have Also Been Unlucky
There are other issues. For example, Boston is 1-6 in the incredibly stupid MLB extra-inning format. You have to think that in a normal extra-inning format, they'd at least have a few more of those wins. They are also 4-8 in one-run games—probably mostly due to their crappy bullpen. They also reside in the toughest division in baseball—and they've gone just 7-14 so far against their division rivals. That's not sustainable.
So, if you mix in some bad luck and some crappy performances—you get a team that's 12 games out of first place in June.