I don’t know how accurate the stats are, but around the bottom of each instance sidebar they have a breakdown of users per day/week/month. I think that’s supposed to pull not from signed in visits but whether they were active by voting/commenting/posting.

Excluding the instances you mention, there’s still a sizable amount of people active if those stats are reliable.

You can see the weekly/monthly stats aggregated in the list view of instances on Lemmyverse:

https://lemmyverse.net/