I can't address your specific experiences with Java, Kotlin, or Scala but even just lambdas in just Java took a ton of wind out from beneath their wings. It ju

I can't address your specific experiences with Java, Kotlin, or Scala but even just lambdas in just Java took a ton of wind out from beneath their wings. It just hasn't shown to be a race to feature parity in practice. Enough of the Kotlin and Scala user bases just really do want a better Java, often in just one or two ways. Personally, and more controversially, I don't think Java getting pattern matching in switches or sealed classes is going to move the needle a ton. (Sorry, Brian!) It's going to be Loom and Records that really change things.