Just played Final Fantasy XI

[Vaer]

With the caveat that I don't think these numbers are actually accurate, but they're all that we have, let's compare to how the FFXIV census works. Again, "active player" means someone who finished the level 65 dungeon. That's halfway through the latest expansion. Around 25%, generously, of players are halfway through WotG according to this data. But WotG is really new, so let's look at ToAU instead - there, it's maybe 40% in 2009 and closer to 30% in 2008. Even CoP in 2009 is basically 50/50 for who's at least halfway through. By the FFXIV metric of "active players" those would reduce FFXI's 500k to 125k, 200k, or 250k, respectively. All of which are well below the 525k listed on the FFXIV census. FFXIV is still clearly the more popular game by a wide margin.

Not that I disagree, but expansion clears is a weird way of comparing it.

In XI it wasn't required to finish storylines to hit max level, you could get to max level without finishing CoP, ToAU, it just made it more annoying and a lot of the areas and features unlock midway through. Due to how long it takes to level back then, I would consider even someone who is still 51+ and at least Rank 5-6 (when the first arc ends and dynamis/zilart unlocks) to be an active player.

In XIV you can't get to max level without going through the expansion so it's kind of a weird comparison.

Completing an expansion fully in XI is somewhat like participating in XIV endgame and we all know how low the participation rate of savage is. It'd be like looking up the amount of T13 or O12S clears right now which most people probably don't even bother doing even though it is nerfed and saying XIV isn't popular based on those numbers.

Different games for different times honestly. The MMO genre was relatively niche back then when XI was in it's prime compared to now (XIV is a mass market MMO, it is designed to get as many people to play as possible, in XI if you didn't like the content they put out it was literally "deal with it") so even hitting 500k back then is pretty good. The mechanics of XI were acceptable in 2004, but they just wouldn't fly in 2018. People in XIV lose their minds over hunts, they would last about 10 minutes in old XI.