Dark matter remains a hypothesis. The velocity issue is real but the dark matter hypothesis is too nonchalantly accepted.
I’ve read several books on it; all have the same structure. First the evidence; galactic halo, velocity of stars in the orbits.
Then the books start talking bout candidate particles and here the argument falls apart. None of the candidates, however cute their acronyms (MACHOs, WIMPs) have ever been observed. Nor has the LHC shown any resonance where we should have found the neutralino by now.
Reminiscent of string theory, where, again, the SUSY foundation is a failed hypothesis.
I would not be so sanguine about dark matter. We’ve wasted 40 years on string theory. Let’s be more cautious with hasty promotions of hypotheses.