Mill's early goal was to be a saner sbt, incidentally also fixing the parts of sbt that are/were unreasonably slow due to questionable design decisions.

Maven has never been relevant to the Scala ecosystem given most of the community has pretty much moved straight from ant to sbt. Only a few Spark related projects stubbornly use Maven, which is a major pain given the lack of cross-building abilities. Slow dependency resolution and inefficient use of Zinc merely add insult to injury.

Yeah... that's my experience with Scala all around - it's abysmally slow, especially if you use any sort of "metaprograming"... (one of the reasons I stay clear of the language)