The delete key should not delete an entire layer track, it should delete the most recent selection, be it a clip inside a track or a piece of content in the library, or a keyframe on a timeline (possibly also control mapping).

Millumin is amazing and in general intuitive and easy to use, but I have found one major element that sticks out as being a continual source of confusion. When I hit the delete key it always deletes the currently active track layer. I see no reason that this would ever be someones intent.