Interesting, I always felt C# was a step ahead of Java, while the JVM was some steps ahead of the CLR.
Of course, other ecosystems have their own versions of this. But Microsoft might be the only one that essentially controls an entire ecosystem and still manages to give devs whiplash.
"Microsoft says you need to start funding your entire product to be rewritten from scratch"
Apropos WCF, well we got JSON and no-one outside of "enterprises" were doing SOAP/WSDL et al any more and it was pretty much done. That's not really a fault of the vendor, the world moved on. At the end of the day, as a software development house you have to make strategic choices, regardless of vendor. And you can still build WCF apps today, sure maybe not in .NET Core, but they'll still be supported for donkeys years by MS, but who'd want to?
Or maybe you're saying it was DOA?
Pretty much. The only time I've ever seen Silverlight apps in the wild were for streaming use (Sky/Now TV for example).