Here is the thing tho, winter is not the slow time at DLR. Halloween and Christmas are in fact the high seasons and have been for a few years now. As OP mentioned, the Monorail closure is partly related to the construction at DD, Haunted Mansion goes down every year for the theme change, and has been happening since I have memory. I always plan for early August specifically because I missed HM one year and never again
It's actually smart of Disney to get all the refurbs needed done in slow summer instead of in the middle of the busiest months of the year. Specially October. RSR breaking down would make crowds horrible in DCA during those months.