OP thinks IDEs are toys. I think Vim is a toy (beyond its functionality as an editor where it is definitely not a toy).
I've been using IntelliJ for at least 10 years now.
If you have used it, you know what I'm talking about.
IDEAVim plugin provides Vim key bindings and Vim editing mode, so it has the best of Vim and an IDE in one application.
Refactoring and navigation in IntelliJ is superior to whatever you can hack together in Vim. You can integrate Vim with a language server but then what's the point? Just use an IDE.
At work we are forced to use a specific IDE. It's a niche programming language not supported by any other software. Vim is not an option.