IIRC Scala also has a decidedly non-trivial runtime library with its own set of abstractions, where Kotlin is basically "better syntax" on top the existing JDK/Android library ecosystem. Writing Scala to deal with an existing Java framework "feels like" working with an FFI, where in Kotlin it's more natural.

Because of that non-trivial runtime when I used it, it also required pro-guard. I like proguard but it comes with its own set of issues. I typically set it up at some point in a project, but I don't want it required as a first step on a new project.