[amaranth]

The extensibility of emacs is insane is why, it really is more like an OS that happens to have editor functionality. I think the only thing that even gets close is Eclipse which has a ton of performance issues which I'm convinced are due to the (enterprise-y) way they try to achieve that extensibility. After that would be the IntelliJ platform, it's usually much faster and nicer to use but also has performance issues and is known for using a ton of RAM.

VS Code is doing well here compared to its competition. It is quite extensible, you can add extensions to it written in JavaScript that can add new UI and make changes to the editor view. It's also much more performant than either of the other two IDEs I mentioned, even after you load it up with extensions to replicate some of the most used features from those IDEs.