Hm, I didn't realize .NET Core had been changed to an MIT license. That wasn't the case when I was working in C# on a regular basis.
My guess is that MS proprietary tooling still sucks out the air from FOSS tools, but I can't speak from experience there so I'll just admit I don't know how the ecosystem has changed since I worked in it.
Visual Studio is definitely still the ideal environment for writing C#, but JetBrains Rider is a solid alternative, and VS Code with the right set of extensions is probably "good enough" for most things.
My guess is that MS proprietary tooling still sucks out the air from FOSS tools, but I can't speak from experience there so I'll just admit I don't know how the ecosystem has changed since I worked in it.