I have much more experience in C# then Java FWIW, so you're welcome to take my opinions with a grain of salt. I've had a couple of really annoying errors with Beam serializers that took me way longer to debug then I thought was worthwhile.

I think it is a worse choice, it's too ingrained in the language and ecosystem to change. That and a couple of other nits would likely make me pick Java over C# or Go if I was starting a new project going forward.