I was under the impression that the term "dark matter" was a stand-in term for something unknown that seems to contradict what we know about how gravity works at large distances.
Cosmologists will tell you more but it doesn't contradict how gravity works at large distances at all - we just see gravity working on something in a familiar way and don't know quite what it is.
Actually, I think, we take it as if it's the gravity we know at work. We deduce the distribution of dark matter using the premise that dark matter is governed by the same gravity law.
If the distribution is actually different or if there's something entirely different, but with the same observable effect, then...