I think I generally agree with you, but I don’t think this is a big grievance. Lemmy.world has enough traction as it is, they don’t really need the “publicity” from join-lemmy.org.
It would’ve been better if they had written this as some kind of policy beforehand. Like if they had written somewhere before this pull request something like “any instance with more than 40% of active users may be excluded from the join-lemmy.org listing”, then it would’ve been more reasonable too.