Some features were introduced in Java before they appeared in C#. But many C# features are yet to be seen in Java.
> best .NET IDE outside Windows runs on Java/Kotlin.
I would argue “in the world”. And it does not matter in the slightest to a user. The best Python IDE is PyCharm, also written in Java/Kotlin. I don’t know which PHP IDE is the best, but I’m pretty sure none of them are written in PHP, and the same probably applies to Ruby.
> best .NET IDE outside Windows runs on Java/Kotlin.
I would argue “in the world”. And it does not matter in the slightest to a user. The best Python IDE is PyCharm, also written in Java/Kotlin. I don’t know which PHP IDE is the best, but I’m pretty sure none of them are written in PHP, and the same probably applies to Ruby.