[isomorphic]

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://solargraph.org/

https://rubocop.org/

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.)