The increase in monthly is just mainly replacing users leaving as the active 6 month seems to be going down the same rate as active monthly is going up. Am I reading that correctly?

Yeah. But the active 6 month is a lagging indicator because it tracks users who became inactive 6 months ago. While the increase in monthly active users is tracking users joining right now. If the increase of monthly active users is sustained for a few months, it'll reverse the 6 month trend as well.

Totally agree that it's ultimately about activity, but the reality is that we need more users to have more activity. I always took for granted the sheer scale of reddit until I joined Lemmy. It takes a massive number of people to sustain continuous 24/7 discussion about a wide variety of topics, which is ultimately what this kind of link aggregator/forum strives to do. And Lemmy users are already really active compared to redditors. There just aren't enough of us yet.

Hey, there's a lot of non tankies arguing with each other too.

You fool.

One works like a forum, the other is a microblogging platform. Definitely not the same userbase.

Mastodon is much older as a software. Lemmy is still under active development, we aren't even on version 1 yet

I would just guess it's because the Twitter-like format is more popular but that's because I forgot Threads was even a thing.