Honestly that site's benchmarks have never been accurate for me in production. But that's how benchmarks work I guess - my bad for bringing up benchmarks! My experience with using Elixir/Phoenix for web applications has been extremely positive performance-wise however, and has surpassed or matched Go, Ruby, PHP, and Python consistently in all production scenarios. For the latter three, the difference has been order-of-magnitude.

It depends on the problem domain as always. If you're doing a lot of naïve single-threaded number-crunching, have fun. But Elixir/Phoenix haven't failed me for web applications, even in very intensive situations. It's the first time I've barely had to do any tuning beyond external factors such as network and database queries (which, by the way, Phoenix's Ecto handles very gracefully and explicitly).

This is my experience with every Elixir/Phoenix app I've worked on thus far. I apologize if I made it sound like some sort of universal truth.