MAU is a number that matters to corporations and advertisers. No one running a Lemmy server is either of these so that metric isn’t really useful or say anything.
Lemmy has been going for 6 years now and it is still new. It isn’t even version 1.0. Success in Lemmy is not what you think it is. The most successful Lemmy server is Hexbear because it stands alone and is growing the community they want.