Granted Elixir's Phoenix framework is not Rails level yet, it's system of plugs and heavy inspiration from rails actually makes it quite useable as a replacement for rails. Also immutability and the associated smaller memory footprint makes it more feasible to run cheaply on services like heroku or aws. Personally, I think elixir is a good boat to jump on to carry us over to the next world of web development.
But! you're quite right. Elixir is focusing on the web application type things that Erlang and the community around it has never much addressed. There's enough interoperability from Elixir to Erlang that you could probably say the ecosystem as a whole is addressing the problem if you squint hard enough.
Side comment, it's been interesting to see Elixir grow since 2013. A lot of folks learn Elixir and then Erlang but I think it's less common to learn Erlang and then learn Elixir. It's led to an interesting situation where Elixir has had to bootstrap knowledge about OTP on its own terms without a large pool of domain experts sitting around. The asymmetry in knowledge--knowing Erlang does not imply knowing Elixir but knowing Elixir implies knowing Erlang--also makes me wonder how the squinting assumption above will shake out long-term. ¯\_(シ)_/¯
On one hand, you have a very similar open source culture to what exists in Ruby. The fact that hex.pm exists alone is amazing. Libraries are expected to work, be documented, and be maintained.
On the other hand, the number of questions that can be answered with RTFM is astoundingly high. Where Erlang has an implicit knowledge requirement regarding OTP and distributed systems in general, Elixir has a much lower barrier to entry in the community.
An Example: On one of my libraries (a db driver) I have received multiple requests for "Add section to README on how to use this with Phoenix". I have a section on how to add to a supervision tree, which from the erlang world is overkill, and I expect users to be able to connect the dots.
That said, the core team is pretty dang smart. There's plenty of OTP wisdom there, and they aren't very quick to give into the mob rule of the community. It's under strong guidance.
Once you get the Erlang->Elixir relationship, I recommend Erlang in Anger.