Agreed that blocking is useful, but the default shouldn’t be having to jump through hoops to make the fediverse usable, especially for new users.
I’d suggest the mirrors of other social media be delegated to their own instance that clearly states that it is a bot-run Reddit or whatever mirror and other instances don’t show them by default.
Those that want the mirrored no engagement content can subscribe to those on those particular instances and nobody needs to have a problem.