The person you're answering said nothing about Phoenix being mainstream, but it's mainstream enough for Discord and Brex to build unicorns on its back.

The reason I've been teaching it myself, despite Elixir being a young, niche language is that I believe it's an ideal choice for a solo-founder or small team trying to build an ambitious web app. It's a tool I personally want to have at my disposal.

Discord is a great model: start with a simple Phoenix app, ship way faster than the competition, build out more sophisticated infrastructure with scale, and then finally rewrite core loops as NIFs (natively invoked functions) that are implemented in Rust. They were in a crowded market with extremely well-funded competitors and they still built a considerable lead in product and infrastructure.

Right. I did hear that Elixir and Phoenix works really well for concurrency