Our backend is currently 50% Kotlin with hopefully 100% when we do a full migration. I think you're already aware of the benefits such as data classes which remove the cruft of normal POJOs. What Kotlin doesn't gift you is a magically better architecture. There's still verbosity in querying a db, serializing JSON, mapping SQL results. Those things by themselves are of course not difficult but add in different layers and abstractions and suddenly the language itself doesn't help that much when your overall flow is just as complicated.

I'm not sure what is necessarily better right now - I am pretty happy with Kotlin (using Dropwizard) and the type safety that comes with it.