3) You have no data on how big the playerbase is
I will just say to this one specific point we do have data, plus we all have anecedotal experience as well.
When the game first came out, xbox1/pc/Ps4 all had the same challenge goals and were all completed (successfully) at the same rate.
However, steadily over the months, the challenge goals for xbox1/pc have declined to the point where these platforms now have just 40% of the ps4 goal. Is this because the ps4 community grew that much bigger over the past months? No.
Anecdotal experience: You cannot tell me that you don't notice that the playerbase is shrinking when you pug. Personally, I have landed into countless empty lobbies (perilous, threatening, routine - doesn't matter) or into a game that is already on wave 3+. These things happen to me with noticeably more frequency as each week goes by. Fairly certain I am not alone with these experiences either.
Like everyone else I'm excited for the DLC, but am still fearful for the longterm viability of this game.