Don't get the Celtics at all as a factor in Red Sox Attention Disorder (RSAD). If anything, success of one local team tends to spur interest in others.RE the Celts, I based my observation purely on my own reaction to Boston sports over the past three years. I haven't paid as much attention to the Sox in the spring due to the suddenly competitive Celts, triggering a RSAD that tends to last long after the Celts are done. I assume others feel the same way, though I don't believe there's that many of us out there (thus only a 3 percent blame assignment).
As so often the case, I think Sox problem is a combination of factors including the two you cite (post-championship, dull team), plus the fact that we have been looking up in the standings without gaining much ground - add that to the intolerable game length and you have a recipe for RSAD.