Lemmy seems to have gotten the lions share of reddit migrants
According to fedidb.org, Lemmy (all instances) has 70,412 active users while kbin (all instances) has 61,811. That's a 53%-47% split - technically a narrow majority, but the reality is that both services have picked up 'about half' of the new users. (I focused here on active users, as the total users stats are badly skewed by the problem a few weeks ago where several Lemmy instances that don't validate accounts were overrun by bots.)
It's not obviously enough to justify Lemmy getting special attention or Lemmy users not being aware the Threadiverse is bigger than just Lemmy.
lowdownfool