I’m suprised by that. I use winsorized sigma clipping with dithering for all my stacks since I have planes, helicopters etc. to deal with in addition to satellites and dark frames are never perfect. I’ve never noticed any degradation in the photometric accuracy of my stacks using sigma clip compared to a simple mean. In fact I would have thought that it would be better since you are removing residual hot pixel outliers. As Grant says, it would be interesting to see a reference that discusses this.