I don't disagree with your observation that the quality of who receives your ideas and how they engage with it is critical for ideas to spread. I would add on to this by asserting that having more people exposed to the content itself makes encountering such valuable reads much more likely and frequent.
>"Twitter is a truly terrible place to present meaningful, long form content"
Agreed, but up to a certain point. I contend that is a valuable place to introduce people to, or otherwise lead them to, a more appropriate venue for long form content. For example, I learned about the work of Lyn Alden through a Twitter thread someone linked, and now I follow her on her website. I am fairly confident that if someone had just linked me one of her long form essays, I would not have been intrigued enough to explore her work. I also believe that the internet has ruined our attention spans and Twitter threads can act as a hook because each tweet is much more digestible than trying to dive into an essay right away. The medium is the message, but set and setting matters as well.
I don't think this is self-evident at all. For one thing, it's not the amount of people who see something that's important for spreading ideas, it's who they are and how much they engage with it. For another thing, the medium really is the message, and Twitter is a truly terrible place to present meaningful, long form content. Linking to one's own blog is something, but it doesn't get around those problems, or hasn't seemed to in my experience.
This is my own opinion, and nothing more than that. It's why I'm not on Twitter. If you see it differently, it makes sense that you are.