I have been developing for about 20 years almost exclusively using Microsoft technologies. I have always been able to fluently code in both C# and Visual Basic. I have gotten push back when looking for work because I don't exclusively stick to one language. However as any programmer knows, after years of coding the language becomes largely irrelevant. I feel like I can efficiently develop in any language even one I have never seen before.
As far as web development goes I have done everything from old school ASP to MVC6. If I had a choice however I would develop nothing but Windows apps. I prefer a streamlined OS environment to the disconnected state of web development.
I am one of those fortunate people who get paid to do what I love. Even after 20 years I still get excited about new projects. I will never feel like a senior developer because there is just too much to know. I strive every day to be better and learn more.