Yeah, in fact we simulate many thousands of galaxies all at once in a big cosmological volume and they all have very realistic rotation curves -- we match these

Yeah, in fact we simulate many thousands of galaxies all at once in a big cosmological volume and they all have very realistic rotation curves -- we match these to the observed rotation curves of galaxies, or use them to make predictions about galaxies that we have not yet observed. See e.g. Fig 1. in this paper: https://arxiv.org/pdf/1504.01437.pdf https://arxiv.org/pdf/1504.01437.pdf