Yes. Because Rails decided what the "Golden path" was 10 years ago, but pales when having to do real-time anything, concurrent anything, parallel anything, etc. also, scaling tends to be expensive.
I will admit that rails ecosystem is much larger and often you have multiple libraries that do the same thing and you can pick and choose and those gems/libraries have been around for a while.
Phoenix you can spin up a SaaS platform with realtime messaging and event handling the way you could spin up a blog with rails 10 years ago.
Is Phoenix really that close to Rails in terms of ecosystem system maturity? I haven't done any real world work with Phoenix. So I couldn't judge.
More often that not most people suggest Y is close to X. And the difference is not that much when Y is already 80% to X.
Reality is that 20% is a huge difference. That takes as much time to reach the previous 80%.
And this could be used across many different subject / domain. It is a common error in comparison.
The only thing that came close or even exceed Rails ecosystem is actually another dead or unpopular language. PHP with Laravel.