There is most certainly a lot baked into the language-specific editors that isn’t in IDEA proper.
That said, the fact that they all share IDEA’s gubbins makes it massively easier to jump between languages and frameworks for small jobs than I ever thought would be possible.
Having a set of tailored environments that also share keybindings and most common features makes for a fantastic (and really under-appreciated) value proposition.
There just isn’t a C#/.NET plugin for IDEA that replicates the Rider functionality, though. Same with CLion and AppCode. They do ship Ruby and Python and PHP plugins. The JavaScript/web dev stuff is baked into all of their IDEs.
Which means IDEA does not contain all the features of the individual IDEs.
The thing is, I’m confident in saying the plugins don’t replicate 100% of the feature set of PhpStorm or WebStorm either, but I’d defer to someone from JetBrains who has first hand experience.
If you're confident, what features don't they have?
I subscribe to all their products so I can verify this :) I'm not sure why they don't have C# or C plugins but my guess is that it's because there's enough extra work in those IDEs that they want more money for them. Rider contains the ReSharper backend, which is a completely different application from IntelliJ.
That said, the fact that they all share IDEA’s gubbins makes it massively easier to jump between languages and frameworks for small jobs than I ever thought would be possible.
Having a set of tailored environments that also share keybindings and most common features makes for a fantastic (and really under-appreciated) value proposition.