Wotlk was definintely more finalized at the point of the leak, but I can't see them delaying DF. 1 week delay wouldnt do much and one month delay (like SL), puts the date at 28-12 and I just dont see that happening with holidays and stuff. Then they would have to delay it to 2023, which breaks the on or before 31-12-2022 and I don't really know how that would work.
I mostly prefer the expansion to be ready tho and so far it seems far from it.