It's comparative, of all social media sites. Which other social media app/site would you consider to be more intellectual than Twitter? Facebook? Instagram? LinkedIn?

stackoverflow is where you go for indepth discussions. Math and physics stackoverflow are excellent, as well as cryptography, security, ancient languages. The mechanism of twitter doesn't really allow for going in depth and it promotes snarky one liners, which even with snark removed, remain one liners. It's a much more noisy medium, IMO, for intellectual exchange.

Stackoverflow isn't for conversations.

news.ycombinator.com

reddit

Maybe if your niche is very narrowly focused like "r/StringTheory" or something technical like that.

I find it much easier to find the subreddits for specific topics I'm interested in than to find the right people on Twitter for those topics. And it doesn't need to be as narrow as "/r/StringTheory", /r/science or /r/Physics are fine too.

I take your meaning but JTN r/StringTheory hasn't been active in over a year. (I will not succumb to the temptation to make that into a string theory joke.)

A niche is narrowly focused by definition.