@yan I have a related question about kapt3. In our case everything works fine and probably not slower than previously. But because we have a lot of AP in the project (databindings, dagger2, autovalue etc) now kapt task while incremental build is overwhelming other tasks by execution time (org.jetbrains.kotlin.gradle.internal.KaptTask length is 17 secs from overal 24 secs of build).
I know that kapt stub incremental generation is not ready yet, but probably we can somehow help you to find some bottlenecks in AP if you can provide some instruction how to better debug AP.