I'm sure you serve them well with Elixir. All these technologies are good enough. You wouldn't be able to build stuff for them in PHP/Ruby/Java? You would, but you prefer Elixir because you think it's superior and thats fine. But even if its superior you have to agree equivalent stuff is being built in 15 other stacks.
Technology choice is a bit overrated imo.
Actually the customer chose Elixir. They found me because there weren't many Elixir developers in my country when the project started years ago. I prefer Ruby for my own stuff which of course is way smaller than customers projects.
