Indeed. Runtime is typically a lot faster than Rails. Response times in dev mode are <1ms which is fun to see coming from Rails :)

My personal dev speed however is a little slower in Phoenix than Rails. And I've been using Rails for almost 20 years and Elixir for 10.

There are categories of problems that are much easier in Elixir (High concurrency, low latency, etc) and for those I would always pick Elixir. If you're planning "just" a crud like web application, Ruby will probably get you to product-market-fit faster. There are (well maintained) gems for almost everything.