Agreed. Was there last month from Dec 10-17. It was great. Parades were crowded as well as the fireworks, but managable.
Was there Jan 15-22 again. Stood in line for Soaring for over 60 minutes (long story, but it was the last day and the EMH visit on the 1st day involved a "passenger of size" and getting off the ride after the safety check). That was the longest wait all week, but planning & EMHs truly helped.
During the January visit, multiple people made comments about the Xmas holidays thru New Year's was super crowded. Lots of foreign guests in January, particularily tour groups from Brazil (everywhere).
It used to be that Christmas in the parks was practically deserted as families wanted that time for family things. That changed dramatically a decade or so ago & now Christmas day is a nightmare. Similarly the week prior to Christmas used to be one of the deadest of the year. That also changed but it's usually tolerable whereas Christmas week itself is not.
However if many schools plan to be out during the week before I'd be afraid plenty of families will use that opportunity to visit & make that week nearly as bad as Christmas week usually is. Not a chance I'd take. Plus remember that the weather in December/January in Orlando can be quite cold. As in freezing. It it the coldest time of year for Florida and a real risk if you plan warm weather things. It may be 80 but there is an equal chance it will be 40's or less. Not the most reliable time to be there. IF the weather holds and you can get the atime early January is a dead time & a great time to enjoy extremely light crowds. But it's a risk and if it's cold it can put a real damper on the visit.