As far as the lack of US Elixir developers, there is truth in that. It isn't that there are not Elixir developers, but that everyone who wants to work on Elixir is already working on Elixir.

Years ago, I knew this engineering manager whose strategy for recruiting Erlang developers wasn't to look for Erlang developers. He found generalists and polygots who would do well in any language, and were willing to learn Erlang, and recruited them, and then taught them Erlang. These are the kind of people who can take advantage of what Erlang/OTP (and Elixir) offers. They can do well with or without typing.

As for defects, the key isn't necessarily what's happening within a module, but how the various GenServer interact with each other. Having low defects within module boundaries are table stakes when working with Elixir. So if you're only measuring defects within module boundaries, you might miss the systemic problems related to interacting GenServers.

How is this different to typespecs and Dialyzer?