You're technically correct, but go to any of the various "This is the Fediverse", "Join Fediverse" and the like, and many, many times you won't even see them acknowledge the existence of Lemmy, happened to me when i decided to jump in last month. Compare amounts of people, Mastodon instances can number in the thousands while the best you get here is dozens, maybe low hundreds. Lemmy is tiny, and it's focus on communities isolates it further from the rest of the Fediverse, the federation doesn't help in the slightest, open Lemmy and all you see is the same dozen posts for days, you don't see on Lemmy posts from the rest of Fediverse because they just don't apply. This is fine, lemme emphasize, but it's early stages and it's undeniable.