Is that really how user-blocking has been implemented?

I thought messages from blocked users were just hidden from view like it is done everywhere else in the Fediverse?

I don’t think this is a good way to implement user blocks… say a user posts some Covid-19 denial stuff… so I write a lengthy reply to inform other users that this is BS, just to be greeted by a “you can’t post this” message on pressing the post button.

Not only should this be clearly visible before writing a lengthy reply, but also is a comment not only meant as a reply to the original author (that might have blocked you) but to inform other readers as well.