As a newb, what editor to use for Ruby? It's one of those languages that VS Code does not cover properly and I can't really find good setup for nvim or emacs. RubyMine works wonders but I'm poor.
Also, why is Ruby "editor responsiveness" (not sure what to call it) so much worse than e.g. Python?
If you're looking for IDE-level language assistance, I can't help you, but since you mentioned nvim: I use regular vim with CoC / Conquer of Completion (vim plugin; LSP server, may not strictly be necessary for nvim), Solargraph (Ruby Gem; language server), and Rubocop (also a Gem) for linting. I previously/still use ALE (vim plugin; Asynchronous Lint Engine) because I haven't gotten CoC+Solargraph to play nice with Rubocop, probably due to something silly.
https://github.com/neoclide/coc.nvim
https://github.com/dense-analysis/ale
My impression with all of this running under MacVim... it's plenty responsive. It can take a while for Solargraph to index everything on startup if you're working in a big project; once it loads, it's snappy. (There's probably a way to cache that startup scan.)