Arguably, for those who want to / have to work in the .NET ecosystem, it is better that .NET is adopting an open source model, even if imperfect.

This actually lessens the vendor lock-in problem and also means less of a risk of Microsoft pulling out of providing security updates for key components.

So far as I can observe, C#, F# and .NET Core as a platform for web development have benefited from the OSS-ification in the form of more dynamic and transparent progress/evolution.

Disclaimer: I'm more of a Python/Django guy.