Is BFA a better or worse expansion than Legion was? Most would probably say that Legion was better. But does this translate to less players logging in, and if so, what proportion are we likely talking about. That’s a much more complex question.
Thankfully, even though Blizzard stopped publishing player counts, we still have some proxies that can be used to estimate them. One of such proxies comes from Wowprogress. These guys track the number of guilds who beat each boss in high-level content.
So, let’s look at those numbers. For sampling purposes, let’s take the number of guilds who beat the easiest boss in each raid and see how the numbers for Legion compare to the numbers for BFA:
Legion:
Eme: 39705
Tov: 23275
Ngh: 20803
Tos: 27116
Ant: 24640
BFA
Uld: 30082
Bod: 22682
Etp: 16705
Nya: 19387
You can see that, first, the numbers always go down during the expansion. That’s expected behavior since Cata. In WotLK and less so in TBC in vanilla, the numbers were growing from raid to raid as the number of people coming to the game during the expansion was increasing. Since Cata, the game follows a different pattern - there is a lot of people at launch, but after a couple of months a big proportion of them leaves the game, and the numbers are declining all the way till the next expansion.
More importantly, you can see that the numbers for BFA are universally lower than those for Legion. In the first tier, Legion has 39705 guilds and BFA only has 30082. In the last tier, Legion has 24640 guilds and BFA only has 19387. Granted, the numbers for BFA, particularly for the last tier, will grow a little, but given how far we are from the release of the tier, this growth will be pretty miniscule, on the level of 3-5%.
So, here we have it. Raider population in BFA is 25-30% lower than that of Legion. And since the structure of gameplay in BFA follows that of Legion with no major additions (Legion also had M+, etc), it stands to reason that the total number of players in BFA is 25-30% lower than it was in Legion.