Same here. Tbh, you're comment just inspired to do a deep dive on VI. Wonder how much more productivity I can squeeze out if I spend an weekend focused on it.
The productivity comes from not having to think about your editing while simultaneously realizing that you can do some complex editing really easily. I use Emacs and Vim both (I prefer Emacs) and It's quite nice when you can streamline some quick code edits.
My latest experience with Vim was helping a friend fixing some import with a React Native project. A quick grep on one terminal (I could have used quickfix) and using the vim fzf plugin to quickly locate the file. VS Code could have done this but the context switching and UI clutter is not great there.
As for emacs, the main advantages lies in the fact that so many great tools already exist there. Things like Occur, Shell Mode and Compilation Mode (relying on Comint, a more general feature for anything REPL), Project, Eglot, and Magit.
I think Vim and Neovim is better suited as editors, meaning quick launch, fast localization of files and fast editing actions. And I like plugins that support this philosophy.
But the goals with emacs is to be a complete platform for anything plain text (with a bit of extra widgets). Almost whatever you need the terminal for can be replicated there, and they will share some common convention. Mail, file manager, music players, feed readers, PKM, PIM,… Tect editing is not so great, but text actions are (Slime is the best example).