yes, on Mastodon when a user block an instance, it's more like a mute than a block. Your posts will still be available to them, but you won't see their content.
The only solution if you want to protect your content from being shared on an instance is to block it at the instance level AND that the instance use Authorised Fetch.
Not all instances have this feature on.
I came to the fediverse in 2017, so nothing to do with reddit or meta or twitter.
The fact is here, we have a choice. So you do you.
On mastodon I have an account on an instance that blocked meta and is using authorised fetch (so the proper way to block a domain) : great, my content won't go there or on any other blocked domains : it's my choice.
I have another account on another instance that didn't blocked meta : great, my content will be shared with threads users and I will be able to browse threads.
Choice, isn't it great?