This guide shows quite different settings form what the wizard did: https://kotlinlang.org/docs/reference/using-maven.html E.g. it specifies

sourceDir

for the Kotlin plugin, should I do that? And why does it replace the execution for the java compiler plugin in the guide?

<!-- Replacing default-compile as it is treated specially by maven -->

How specially? What? What does that mean? Why is the documentation so bad?

The goal of that block is to make kotlin compilation executed before java compilation. It is explained right above that sample.

thanks Ilya, this finally sheds some light on this!