The strongest evidence that something like MOND isn't the answer is that in some galaxy collisions, the visible matter and the dark matter appear to separate: the collision disrupts the visible matter and the dark matter appears to pass right through, uninterrupted, and we see galaxy remnants that look like they don't have dark matter. If MOND or some other modification of gravity were the answer we'd never see this kind of sorting.

See, for example, https://www.caltech.edu/about/news/dark-matter-flies-ahead-o...