dark matter is irrelevant. The speed law is empirical (whether or not you explain it with dark matter) and the first poster points out that the constant edge rotational rate falls out from that, and geometry.
It is relevant when you compare models. All I asked is how accurate both models are. If Dark Matter is more accurate in predicting how galaxies move and shape then it is obviously the better model even if a simpler one also exists but it's predictions are worse.
You can't simply say "this model also predicts that" without giving on how accurate it does predict and comparing to existing models. Otherwise we'd be using flat earth models for building bridges and planning ship routes.
The original poster's original comment didn't make claims about the validity of dark matter, it was only in a different subthread that he talked about dark matter directly, challenging it. The original comment's content is invariant on how you derive the distribution of stellar velocities.
