This is kind of the point, though. So many unlikely (but not impossible) events need to occur for this race to go from non existent to maybe if you squint hard enough and don't think logically or look at playoff odds you can find a reason to have mild concern.
That would still leave the Sox in a position where they're a vastly superior team, have the 2nd largest division lead in baseball, and a very cushy upcoming schedule. Even if that were to happen, I think the Sox would still have playoff and divisional odds in the 99% range. So, no, I would not be worried. You've essentially just described the position the Brewers are in now (but with 4 extra games off the schedule, which would matter) and I don't think you would say the Brewers are in real danger of losing the NL Central, would you? And they have a much better team chasing them than the Sox do.
I'm not smart enough to do the math on this, but the pace Cleveland would have to outplay the Sox by (if extrapolated over 162 game season) to make up 9.5 games in a 6 week span is so extraordinary it's not something I spend anytime worrying about. And when there are objective measures like playoff odds, particularly this late in the season, giving Cleveland a 0.1% chance of winning the division I see no reason to go against that.