There are 87 000 players in Quickmatch. If I am correct, QM was introduced in 2017 October and first month had 20 000 players ranked, next few months doubled it quite fast. So take 40 000 players got ranked for years of 2018 and 2019 - so its roughly 1500-3000 players per month. For previous years its around 13 000 accounts creations a month. If 2019 ends I will check how it changed for this year.
There are different levels of activity. Some play only single-player, some occasionally real-time, up to players who visit at most every 3-days and are considered the most active in Warzone. My own estimate is that, there are no more than 20 000 very active players (excluding players who are new). But there could be up to 100 000 individual account visits to the site.
To be fair, even before QM 90% of RT games were Small Earth dumbness, ROR, Imperium Romanum and failed diplos/huge FFAs that never filled. I rarely ever check what's happenig in MD open games so I don't know what to say about it.
