I have only been to WDW over Christmas week a few times, but i have been over other major holidays many times, and there is much similarity.
No matter when you visit WDW, the in-park crowd peaks between roughly 11am and 5pm. During those hours, expect long waits for major attractions. Also expect LL's to go early/be limited.
On the other hand, MK was open until 1am on NYE. The last hour the park was open, just about every ride was walk-on or near walk-on.
I've repeated visited over holiday weeks because the parks are open for extended hours, and Ilike the flexibility that we get with extended hours.
If your touring style is to sleep late, leave early, you want mid-day waits to be short, and you want prices to be low for food/hotel/park tickets/LL's, then holiday weeks are not a good choice.
One key to getting a lot done is to shift our touring style. If it is a holiday week, we generally avoid a few rides, like 7D. We especially avoid rides like 7D between the hours of 11am-7pm unless we have a LL for them. When it comes to paying for ILL's, we are very selective, or rather we don't buy them.
What we try to do is to zig whenever the crowd zags, whenever possible. This takes some thought and involves some choice. A small way to zig is to avoid eating lunch at noon, actually 11:45-1pm. Another small way to zig is to do things out of order. Instead of eating cie cream after lunch, we eat ice cream before lunch. Often ice cream is our lunch. At 11:30am, there's a long line at all the QS lunch places, but no line for ice cream.
Mind, if you are into preplanning WDW visits, and are visiting WDW so you can try to most-popular food/snack/new ride, then this type of touring might not fit with your touring style. Flexibility is key to making it work.