With a blocklist, the user is putting their trust in an unnamed group of people with essentially no accountability. With defederation, the user puts their trust in admins they can talk to, with a public modlog to explain every decision. Youβre proposing to take the same amount of control away from users, but with less accountability.
They are both essentially the same thing except u decided to call one group of unnamed people Admins and suddenly they have responsibility and authority.
You can have the federated blocklist people named, decisions for adding to list public and explained. That way it would be the same as with admins