Could you point out where do you get your data from? Anything to back-up your claims that Rails is in decline and Elixir/Phoenix is growing? For a time not long ago I was heavily into looking for an Elixir gig, but couldn't really find offers, while there were still tons of offers for Rails development.
Sure, but thats a weak argument considering Ruby on Rails is considerably older than Phoenix and adoption is in decline while Phoenix grows.