“Ruby developers” should not exist. You use the right tool for the job. It’s great to have an option that is (partially) familiar, but as a developer you should not be limited by syntax choice.
Why would rubyists need elegance in a different language for perf? Do what everyone else does, and write a C extension.
The point is that they / we don't want to write c.
Speaking personally, I don't want to write in anything else but Ruby. If I have to code in something else, well, anything's fine. I don't want "elegance" in that language. I don't need other languages to try to be Ruby. I already have Ruby. I just want to get it done so I can build on that work... in Ruby.
I just don't understand why other people seem to think Ruby isn't enough.
I like Ruby, too. But Crystal is like Ruby, and better in many regards. Performance is a huge issue with any computational intensive tasks. Crystal's static typing also avoids many simple errors you would only catch in Ruby with an extensive spec suite for many edge cases.
This is a Crystal discussion, and I hate it when Crystal people show up in Ruby discussions and talk crap about Ruby so I won't argue against you, other than to say that Crystal is only like Ruby in that it's syntax is superficially similar.