[passer-by-123]

The push to new technologies are not based solely on performance.

Rust brings a type-safe and memory-safe guarantees. Elixir brings concurrency and functional concepts that lead to clearer code. Even node.js has the benefit of ubiquity. Even if you want to debate those claims, those are perceived reasons for people adopting those platforms - just ask them. Having a more scalable and performant platform is just a nice bonus.

It is also misleading to think that performance impacts only the user experience. No, it drastically affects the developer experience too! Over the years the Ruby community has struggled with performance issues. Your application takes a long time to boot? Let's introduce a tool like Spring that works only half of the time. Your application cannot handle blocking requests? Let's push our whole design towards jobs. View rendering is slow? Let's add cache layers over cache layers (aka russian doll caching) and then good luck debugging cache expiration issues.

Even running tests is unnecessarily slow in Rails. When one test is querying the database, another test should be running. I am not talking about multi-core concurrency, just simple IO-based concurrency. Extra points if a language can give me CPU concurrency too!

Those are long term issues that impact the developer productivity and increase the maintenance burden on your teams. That's without taking into account other issues prominent in the Rails community, such as abusive use of monkey patching and global state. I moved away from Rails not because I wanted performance but because I wanted simplicity and long-term productivity.