I don't think lemmy is still growing. I might be wrong but this graph https://fedidb.org/current-events/threadiverse
is trending down and i've seen a lot of smaller magazines/communities that haven't had any posts for 1-2weeks by now.
I try to help that problem at little but i doubt lemmy&kbin has >100k active users right now.

The dip is attributable to kbin which has some weirdness around active user counts, largely because they don’t keep track of them, so I’m not surprised that their numbers might vary somewhat over time.

Otherwise, yea, it’d be accurate to say that the migration wave has come to an end. Mastodon went through multiple waves over the years so we’ll see what happens from here. I for one am rather happy with how lemmy (and kbin) have turned out and am not desperate that a hole bunch more people come over.

My biggest concern isn’t that there isn’t more cross talk between lemmy and mastodon, and that’s because the fediverse is yet to actually do a good job of making the boundaries between platforms thinner. There are many conversations going on in parallel that would be happy to connect but can’t because the fediverse hasn’t worked out a way to make that work well (yet).