I will leave my personal opinions down here in the comments.
On one hand, no harm is being done. It’s possible this is a temporary situation due to ClubsAll being young and in development. Also, all our data on Lemmy is public anyway; we cannot stop others from scraping it.
On the other hand, on principle I don’t like one-way interaction and the way ClubsAll presents Lemmy content as their own. It feels deceptive. Defederation would be a symbolic way to protest that behavior.
I am torn. At the moment I am slightly in favor of defederation.
I like this. I will put a reminder on my calendar to check on ClubsAll in a few months. If more users complain about it then we can reconsider the approach.