Scala and Groovy both have about 2% mind share on the JVM. I wouldn't call that "immense".
Are you counting java in that percentage? What is the percentage of scala out of non-java jvm languages?
It seems to be tied with Groovy at the #2 spot (about 2% each).
Maybe 2% developers.
Mind share ... are there any great minds left in the Java ecosystem? Doesn't feel that way.
Scala and Groovy are used for two totally different use cases. Scala is used instead of Java as a systems language for building systems, whereas Groovy is used as well as Java for testing Java classes or calling them from Grails. In theory we could use Groovy as the dynamic language for Scala, but because of its type inference and syntactic tersity Scala doesn't need a Groovy.