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.
'spite' mostly
You haven't been paying attention
you have bats in your belfry
Ooh you got any more insults?
Nope
Is spite in quotes because you don't believe in what you're saying (not the correct word to use) or you're unsure spite is an actual word?