Maybe Twitters "UI" is so messy is because its text. People can make up any convent they want. Like signing posts with ^.
Notice how if you click a tweet in the timeline, you do not get a overlay to show the conversation. Nope, it push away the tweets below to make room. Then when you click anywhere else on the site the conversation collapse back, shifting the position of surrounding tweets once more.
Similarly, the only way to see a image full size is to basically drag and drop it into a new tab. If you click it you just get a floating view that barely make use of 75% of the screen, with a copy of the related tweet below it.
To make use of the twitter site i find myself liberally middle and ctrl clicking timestamps and similar to throw tweets into new tabs.
And their latest "innovation", embedded tweets, basically wrecks their own conversation view. Now you can't click a tweet and see the reverse timeline. Nope, you have to click each of them in turn to dig into the dialog.
I've said all this but either is INIFNITELY better than twitter, especially twitter's standard web client. TweetDeck makes the thing barely useable.
I'm fairly technically proficient and I have a hard time figuring out how to "onboard" myself to Reddit and to understand the whole system. It's relatively intimidating.
If we want to stick to text-only, I think HN is actually a better example. Of course, Facebook is really the pinnacle of broad accessibility.