Based on data from https://fedipact.veganism.social/ it seems that the majority of instances blocks threads.net. I'm sure there's Lemmy instances with either approach that have slipped through the cracks as the list is a work in progress.
The percentage of users doesn't correlate to instances as the biggest instance on the Lemmyverse has roughly 3x the users of the second largest, a NSFW instance, 4x the users of the biggest "niché" instance and 5x the users of what I see as the second largest general purpose instance.
Maybe that and the creator of Mastodon actively rolling out the red carpet for Zuck
Yep. Meta's convinced him that this is a huge victory for Mastodon -- and a good way for him to achieve his goal of getting Mastodon to 100,000,000 users.