Doh Phoenix and Elixir are trying to do all the best to help developers be productive, when you are a technology that promises such a huge scale you need to introduce practices that need to be decoupled => bit slower for developers.
Good example of this how a “model” writes to database. Module (with schema) need to call a changeset, changeset call repository, repository writes to database (example). That’s 3 manual steps where in Rails you have in in one.
Phoenix & Ecto work that way because 1) Elixir is functional, and 2) ActiveRecord mixes a lot of concerns that suck in the longterm.
IMO the real thing holding back Phoenix/Elixir is deployment & operational issues. It's being worked on a lot with Distillery, but from what I understand there's still a lot of kinks to be worked out.