Except, it wasn’t.
It was about the same in Japan and it was about 10m. More WW, the PS4 was around 48-49m when XV launched WW and PS5 is around 38-39 when XVI launched.
Why people are still doing this?
Because for a title like FF, the size of the install base isn't really relevant, outside of it being abnormally tiny ala WiiU or something.
FF isn't something that people just pick up because they see it's out, it's a premiere core title that's meant to sell systems and galvanize the base.
It selling what it did isn't a failure but it's also not a roaring success.
For the profile and legacy of the series, its squarely mid. And that's just the launch.
Legs will decide how it's seen as an overall performer for the series.