I would describe samatha as not noticing things other than the object of meditation, and vipassana as not missing anything about the object of meditation. In samatha focused practice, the object is so small that it has very few details. In vipassana focused practice, the object is so large that it excludes hardly anything (most common is to allow everything into the focus except the distracting interiors of discursive thoughts). But even focusing on a very simple object requires insight into the quality of sensation, and even excluding just distracting thoughts requires a basic ability to concentrate, so even in these exaggerated practices they do need to work together.