I have spend most of my career doing Java6 JEE6 and modern Spring and it all feels quite modern. I did a lot of C# at University and it is a good language and platform but I don't think it's better than Java. New / modern Java is fine, it's old java that you want to avoid.
imo C# is an improved java, but C# open source ecosystem is just anemic compared to java.
By that logic everyone would still be using Cobol or Fortran for new development. Moreover neither Rails, Django, or Grails are brand spanking new anymore. Those projects are mature. If you don't want to stray too far away from the jvm comfort zone, Grails is actually built on top of Spring and Hibernate and it's still maintained by the Spring team.