Look, I do understand the numbers, but this year the simple fact is that the Sox don't have enough great fielders and/or good hitters to provide 12 everyday lineup players. Dalbec is in horrible slump right now and is a lousy firstbaseman, but hasn't missed a game in like forever. Chavis is playing and helpless--again.
My point remains: the Sox currently don't have enough good players to justify, say, 13 or 14 players on the big club. So it just makes sense to have extra relievers, especially when your rotation is struggling.
And, FWIW, to me it's silly to have a bunch of position players who probably won't get in the game anyway, especially on a team with a DH.