Signal is known to store two points of data per (hashed) phone number: the first login date, and the most recent login date. The second point is sufficient to get a user count.

Having a "most recent login" doesn't prove someone is an active user. I use it about once every two days, am I also an active users? Compare that to WhatsApp which most people use multiple times a day or even multiple times per hour, and you get the picture of how popular or lack thereof Signal is by comparison.

Like I said, a lot of people have Signal, but very few use it as their primary messenger on a regular basis, and more of a "it's just there in case one of those tech nerds who told me to install it decided to message me on"

"I use it about once every two days, am I also an active users?"

Yes. I think your definition of "active user" is non-standard.

Is it? My definition of active, is "do you use Signal as your main messenger or in that ballpark".

If you only use it a couple of times per week you're not really an active users when messenger apps on average get used multiple times per day.

So I don't think I;[m unreasonable at all to compare Signal to the average messaging apps in term of screen time.

Yes, that is definitely a non-standard definition of "active user". It's not really a relative term - if you're signed in and sending/receiving messages, you're an active user.

By your definition I don't have any active messenger!