Speed would be nice, but more than that I want it to also manage Ruby installs. I’m infuriated at the mess of Rubys and version managers.

Mise is the answer to this. I no longer use chruby/rbenv/rvm. And it manages multiple languages, project-local environment, etc.

what exactly is your issue? I've been using rvm for a decade(?) without any major pain. Cross-language tools such as mise or asdf also seem to work ok.

I can relate to the "I wish we didn't need a second tool", but it doesn't seem like much of a mess.