Author here. What most people don't realize is that "I hate programming my build." is a symptom of your existing build tools making programming your build dangerous and risky endeavor.

For example, in Maven you typically extend your build in Bash scripts + maven-exec-plugin, Ant script + maven-antrun-plugin, or custom Maven plugins entirely. None of these are "nice" programming environments, with proper IDE support, typechecking, introspectability, and so on. Writing lots of logic in Bash or Ant is risky, so you would be right to minimize writing code in it

Similarly, in Gradle you extend your build in Groovy/Kotlin, but it's a kind of "weird" Groovy/Kotlin unlike anything you'd write in application code. For example, your IDE support in Gradle-Kotlin is much worse than what you get in normal-Kotlin. Despite Gradle-Kotlin being the same language and same IDE, it's a much worse experience writing it, it's much easier to make mistakes, and so you are right to minimize the code you write in it.

In Mill, the build scripts are in Scala, but that's not the important part. The important part is you write normal code using classes, methods, and overrides. IDEs are very good at navigating classes, methods and overrides, and developers are very familiar with working with classes, methods, and overrides. And so build code in Mill feels as comfortable as your application code in Java/Scala/Kotlin: same quality of IDE experience, same typechecking, even can use the same Java third-party libraries (if you wish).

So it's understandable you hate programming your build. In Maven or Gradle or SBT, I'd hate programming my build as well. What Mill offers is that you can program your build where necessary without the hate that comes with doing so in other build tools!