phoenix's channels (for realtime) is the only multiclustered websocket solution with long polling fallback that I know of that will scale to thousands of users out of the box. My startup uses websockets and its never been a bottleneck vs the headaches I've deal with doing similar stuff in nodejs. its just an absolute unit for doing realtime.

And now they have liveview which takes that and builds on it to accomplish magic.

rails has done great things but comparing it to phoenix on realtime stuff is like comparing a moped to an f16

Then there's realtime. phoenix channels is the standard. everything else is a janky copy thats issing one or more factors that make it so good. elixir users lightweight threads so there's less overhead per connection which means you can run WAY more connections on a single machine. Live view takes this further but allocating a persistent process per user on which state can be synced to the frontend without writing ay javascript.

ruby on rails has more and better gems when your'e starting out but once you get some traction, maintenance on an elixir app is much easier due to it being functional.