Agreed - though I find that is the hardest part of learning a new ecosystem. Learning Elixir "the language" is one thing. Learning the entire ecosystem, including the idioms (from simple things like "how do i physically structure my project" to complex, like "how do i structure my modules") and the unique ways to solve problems within that ecosystem is another.
It's especially important, in my opinion, when Elixir/Erlang/OTP introduce ways of doing things that are so foreign to any other tech stack. For example - if I want to read a file and use it for input throughout the lifecycle of an app, does it make sense to use a Genserver? Do I then supervise it so that if it dies for some reason, my app still functions? No other tech stack that I've ever seen even touches on anything like this. There are a lot of those kinds of things that various books touch on, but none that I've seen which really pull it together. The Little Elixir and OTP Guidebook fills in a lot of great context, as does Designing for Scalability with Erlang/OTP
In general, this is the area where I see the most need. I know that Johnny Winn has talked at length on Elixir Fountain about the "Intermediate" level Elixir practitioner. Or rather, the lack of depth in that category of expertise within the community.
I have not yet - I'll take a look.