MOND is an entire family of theories, each of which accounts for maybe one or two edge cases by tuning specifically to them while handwaving the rest away. On the contrary, dark matter is just matter that is dark. There are plenty of questions about why it formed, or why there's so much of it, but in principle stuff that doesn't interact with the forces we work with isn't out of left field.
Once predicted, it's easy to see how the motions of galaxies works perfectly with some extra stuff in the mix. The differing behavior of spiral vs. irregular galaxies, as well as scaling to clusters and superclusters, falls right out of dark matter. You could predict pretty much everything we've observed the minute someone told you about dark matter, even though the concept was formed before we had all the data we have now.
Once predicted, it's easy to see how the motions of galaxies works perfectly with some extra stuff in the mix. The differing behavior of spiral vs. irregular galaxies, as well as scaling to clusters and superclusters, falls right out of dark matter. You could predict pretty much everything we've observed the minute someone told you about dark matter, even though the concept was formed before we had all the data we have now.