If so, then sounds okay, as long as the person knows they have been blocked, would suck to write a well written comment in reply to someone who blocked you, and unknowingly your comment is hidden for everyone because you don’t realize you were blocked.

That's exactly what should happen. If someone can just instantly know when they get blocked, nothing stops them from instantly signing up with alt account to continue bitching at someone.

This is less of an issue with centralized social media, but with federation you absolutely should take measures like this to curb at least some portion of targeted harassment.

And if you bothered someone enough for them to block you, not being allowed to stand on their soapbox anymore (not being able to make comments on their posts visible to everyone else) is a really weird thing to worry about.