I will say, the desire from a member to block another member doesn't have limitations. They undoubtedly want to see absolutely nothing from that member (topics, replies, quoted replies, etc). The challenge definitely is topics where you lose context once certain posts are hidden, but there's no avoiding that if you want to hide certain members and see others and there's a topic they are both participating in.
In this particular use case, it just seems especially odd to hide the OP's post (topic's first post) but not the topic itself. You have zero context if you hide OP, so why would you want to see any replies to a first post you can't see?