I think that if a platform wants to support long-form content, it needs to make design choices around long-form. It can't be a short-form content UX with an arbitrary limit removed so that long posts can be created, if they're going to be displayed and interacted with in the same way as 280 character tweets.
Some design choices that made Tumblr better for long-form posts and discussion: Being able to tag a post without writing the tag inside the main post body, so posts can be categorized without messing up the content. Text formatting support. Media can be inserted into any part of the text instead of forcing them to appear at the bottom of the post. Q&A. Post archives. Custom blog theming. One account can have multiple blogs to organize content. Replies show the context of what they're replying to when shared. Support for commenting on posts. They combined these effectively with short-form design like the centralized feed of posts and interaction buttons.
Another reason I prefer Tumblr over Twitter is because Tumblr's format makes discussion most visible, while Twitter makes soapboxing most visible. Tumblr's design has flaws, but it's the best example of platform design that balances long-form, short-form and discussion in my opinion.
What are the odds that the random website it gave me was my physics study guide in high school? The Hyperphysics website