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You're human; THE most adaptable creature known. Adapt!
I'm not saying that twitter UX is perfect, or even good. I AM saying that it is usable.
The amount of stuff your brain has to filter in the form of user name, user tweet handle, additional tagged handlers, UI menus, UI buttons for replying, retweeting, liking, etc on every single code snippet makes your brain work way more than it should to read a page of text.
Just imagine if I had written this exact text in 3 separate HackerNews comments, and prepended each with a 1/ 2/ 3/ text, in addition to all the message UI, it would have been more difficult to read than a simple piece of text.
Because that's what I'm getting from you.
Yes, their UI sucks. No, they haven't fixed it. I would not be surprised at all if that were due to necessity rather than incompetence. Even tiny changes at that scale make large differences.
And, honestly I would not be surprised if it were incompetence, either. The skill of the silicon valley developer (as demonstrated by the commenters here) does not impress me even a little.
This website is full of employees (and ex employees) of Google, Facebook, Amazon, Netflix, Twitter, and any other company that has done stuff at global scale.
Scaling provides constraints, we all understand that. The interface being completely miserable to use is not because of that constraint.