I'm not sure how suggesting that Lester and Beckett turning it around is not realistic?
Lester has thrown to a 2.45 ERA over his last 4 starts. Beckett had a stinker vs CLE, and even with that bad outing, he's got a 3.43 ERA over his last 7 starts. Projecting them to continue pitching like they have been over the past 5-7 starts is absolutely realistic. Not sure how that wouldn't translate.
As for the bullpen, no they're not going to post a 1.98 ERA this year. They have a team 3.80 ERA. As bad as the 1st month was, and as good as May has been, I think they will be right around the average of the two, which is a 3.80.
And it's not as though the Sox RP are just getting lucky. They've got a 3.80 ERA, a 3.90 FIP, and a 3.67 xFIP, a 76.1% Strand Rate, and a .290 BABIP. None of those numbers are outside of a normal range.
So expecting a 3.80 ERA (which is basically what UN said) is very valid. And that would be a good bullpen (Sox had a 3.67 ERA in their pen last year, which included Pap and Bard).
And again, as UN said, Melancon, Bailey, and Bard will all be in the pen by the end of the season which will be upgrades.