Nostr.band is pretty close to the truth. It misses a few because it's only reading a few of the most used relays. But that's just a count of npubs that are subscribed to your npub.
There's a lot of npubs, but only about 9-10k daily active users.
Discussion
Yeah nostr.band is very good but I just stopped caring. On nostr follower count doesn't really mean anything and can be easily manipulated by any wannabe inFLUenza. Zaps are the signal 😉
Zaps and replies are what keep me going. I say some shit on X and it gets a couple likes and maybe a repost. I say some shit on Nostr and it starts an all day discussion that everybody jumps in on. I love it!