In twitter "public" is not a label for a specific type of audience, it's the name of common use of a work being public/generally shared with the world. The feed/timeline you are referring sounds awfully similar to Facebook/Instagram/etc which are notorious for being walled gardens where what you say it's true.

Okay, but you are aware that "public" means everyone? e.g. the blocked persons friend or frankly second account?

What you want is a list of friends that you share your posts too, but then you wouldn't need social media if you weren't talking to strangers.

> If I block someone, they no longer have access to my timeline.

Yeah and I instantly think "what if they create a new account" and your whole protection instantly fails.

Blocking is barely good enough so famous accounts dont publicly mock you with all of their followers.