While I think, that you might be right and JS really has a ton of support, imho, the DX is not that good, because of the dynamic nature of JS. Static analysis fails me all the time. That's why we have TypeScript, which takes away a lot of the problems and risks and makes working with JS safe. I use WebStorm and IntelliJ IDEA for working on web projects, and I love them!
As for system languages, C and C++ should have the best support overall. Most important software is written in C or C++. You are most probably sitting in front of an OS, which was written in C/C++. There are CLion, Visual Studio and XCode, to name a few.
As a new-comer, though, I'd say Rust should have an even better experience. It's compiler does a lot for you and outputs really helpful errors and guides how to fix them. The only downside is that it has rather bad IDE support, because a lot of important features are not yet implemented (lifetime visualization, borrow highlighting, wide-spread debugging support, etc.). Good IDEs which support Rust include CLion and VSCode.
To put it in a nutshell, I love the JetBrains products. That's why I would say, if you use any of their products, you will have an awesome IDE and really good DX. That includes Java, Python, JS, PHP, C/C++, C#/VB.NET, SQL, Ruby and soon Go.
EDIT April 2020: I improved the text and updated the content a bit, without changing it too much. Also, I added Rust to the languages.
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