JVM is great. I think it gets a lot of love (in comparison with .NET Core which is IMHO as good as JVM). In this one, you see JVM everywhere except desktop apps.
Then, there's Java itself. As a language, it really isn't as modern and doesn't provide much what isn't already available in C#, Scala, Kotlin, or even PHP or TypeScript. And it doesn't provide some things that other languages have. So on this scale, once you know Java, you can be productive, but I doubt you will be more productive than someone who knows C#, Scala, etc.
And then, there's Java culture. Plenty of Java devs (mainly in J2EE, Spring world) don't develop in classes, they develop in design patterns. AbstractFactoryStrategy, complete abstracting out databases, five layer data models, classes for things that should be enums. It's a matter of taste, you don't have to do it (Android devs don't do this that much even when they use Java). And I think all the coolness of modelling, UML, etc. is over.
I think, you can be productive in Java (if you use it a bit like PHP). I think JVM is fantastic. For me, I am 8 years in Clojure world and I wouldn't go back to design patterns, writing (in Java often generating) dozens of lines of code just to insert something to the database (entity, mapping, repository, business logic layer, etc.) when in Clojure, this would be three lines (defn, schema check, insert).