The beauty is that it's not an either/or thing since it's possible to use both in the same app. Kotlin needs less code, making some kinds of classes (like data and event classes) trivial to create since much less boilerplate is required. Moving those from Java to Kotlin is an obvious approach to Kotlin-ize Android apps - I've started one of my apps on that route, mostly as learning exercise, and have been satisfied with the result.
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