The entire .Net Core ecosystem is in a weird funk right now. I think it will be a few years before everything is transitioned over to .Net Core and settles down.
Still if people have the mental capacity and time to spare, right now seems like a great time to getting started with .Net Core, and especially on Linux and Docker.
That said, this article makes a lot of mistakes. Xamarin and Unity use mono not .net core.
.Net core isn't ready to bet the farm on. The cross platform tooling is still too weak atm. Its a huge headache to get profile data on Linux.