Also, why is Ruby "editor responsiveness" (not sure what to call it) so much worse than e.g. Python?
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.)
Doesn't quite get you to the level of RubyMine in terms of smart-ness, but I find it's close-enough in practice. And I also highly recommend using TreeSitter for syntax highlighting if you're gonna go the Neovim route -- for whatever reason, I've found regex-based highlighters to be unbearably slow on even medium-sized ruby files.
I also work on a project that uses Rubocop for linting which is nice since it gives you some Prettier-like auto-formatting.
There may be some more goodies to be had (e.g. debugging via nvim-dap), but I haven't dug into that yet. As it stands, I'm pretty pleased with my current setup.
I have no idea what you mean by editor responsiveness.