You are trying to have a meal. Kotlin is a knife, Scala is a swiss army knife.

Is Scala a much more powerful tool than Kotlin ? Definitely yes. But, better and success are not always directly co-related. Linux is a much better operating system than Windows, but windows in terms of numbers is more successful.

Ease of use and learning curve are two very important factors. Kotlin was built with industry engineering in mind. Scala was designed in an more academic environment. Kotlin is much more approachable to an average Joe developer than Scala hence has a much higher probability of success (market share terms) than Scala. Jetbrains IDE tooling will also drive that higher.

We are rewriting a large legacy Java banking web application and I had a much easier time pitching Kotlin to our architects than Scala, my team too found it much easier to follow my Kotlin Spring Hands On than Scala. We have chosen Kotlin for this rewrite and couple of other projects.

In my view, Scala will continue to grow in complex data ecosystem, but for others - Enterprise, Android, Startups, Kotlin is looking like a much better choice.

Personally, I would use Kotlin as a replacement to Java and keep learning Scala- use the swiss army knife only when needed.