I can say for certain that is not the choice of the Community Team. They would MUCH rather have an organized D4 page so that they could easily collect feedback in one place, and also monitor accurate D4 engagement metrics. Mixing it all together makes the job for Community a heck of a lot harder.
While they were happy to discuss a specific example, they don’t take only 10k paragon players as references. They collect a HUGE amount of data from everyone playing the PTR to use for metrics. Will they look at the extreme cases? Sure? But that is not the core reference for them. I think they just don’t really explain their methodology to us very well.
Regarding the Xmas thing. She personally did on her own Social Media.
The official messages come from the actual Blizzard accounts. Diablo used the general Blizz xmas message on the Twitter feed. https://twitter.com/Diablo I am guessing a decision was made not to do something specific for the Diablo Franchise.
For WoW they did the Twitter thing, and a 2019 wrap up post. https://us.forums.blizzard.com/en/wow/t/thank-you-for-a-great-2019/395559
OW did the Twitter thing, and a live stream yule log. Nothing on forums.
Hearthstone did the Twitter thing - retweet of the general Blizz xmas message. Nothing on forums
HotS Twitter used a fan made Holiday Image. Nothing on forums.
SC I don’t actually see anything.