Seems very anecdotal indeed - I have trouble believing that Ruby is mostly maintenance now or that a significant portion (say, >5%) of Ruby devs have switched to Elixir.

I've been in several companies that do both Rails and Phoenix. Everywhere Rails is used mostly because management doesn't want to fire loyal and good programmers who aren't interested in learning Elixir/Phoenix. A second, and very often cited reason is that their Rails app is working fine and they don't see why should they rewrite it.

Both are completely fair.

Not going to claim my anecdotal evidence is universal -- just adding a data point.