[zaarn]

Highschool definitions of velocity don't really apply once the distances involved grow beyond a couple light years. Atleast not without corrections for stuff like relativity (which has been measured and confirmed to exist by simply observing curvature of light over the sun.

Or did the entire community of astrophysics simply ignore high school physics in favor or something vastly more complicated because reasons?

[dnautics]

Even at galactic scales the correction is not that great. I don't thing the OP's claim is that they are exact to say 3 sig figs but more like exact to within an order of magnitude

[zaarn]

But how does the proposed model compare to the accuracy of the dark matter model?

In physics, how well your model can predict past and future states from the current state is rather important. Though future states more than past state but any model should be able to also somewhat agree with it's the past it generates.

[dnautics]

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.

[zaarn]

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.

[dnautics]

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.