The ecosystem is what drove me away from C# (as well as not wanting to do enterprise work). I started dabbling with Ruby and Node and the sheer number of free third party libraries blew my mind. C# simply didn't compare.
This is a very weird criticism. I'm a Ruby dev, but I spent eight years working with C#, and I can't remember any times where a Ruby gem was more readily available than a NuGet package.
If anything, I'd say there's less choice in the Ruby world, especially in the data science and ML fields.
Depends. I think it's valid. There are a tonne of libraries available in both ecosystems but I find they tend to optimize for different things.
I came from the Java ecosystem to .NET and even they are different. The .NET ecosystem was held back a little by the lack of embracing open source at the beginning and being super commercially focused. So things like finding a good library for easily working with PDF will set you back $400 rather than just using the defacto library that everyone has used forever and is free. I've encountered that with PDF libraries, rules engines, workflow engines, job scheduling libraries.
It's still a decent ecosystem, it just is different because of its roots.