To shore up my point from earlier, I was specifically talking about how we spotted Neptune without ever seeing it by observing the stuff we could see, just like

To shore up my point from earlier, I was specifically talking about how we spotted Neptune without ever seeing it by observing the stuff we could see, just like how we identify Dark Matter. Looking back I definitely didn't make that clear, plus the fact that we already knew that normal matter existed muddies the waters further. Now to your points specifically. Dark Matter needs 0 modification to explain superclusters, normal clusters, and individual galaxies all at once. The basic principle is hard to swallow, obviously, but it made predictions about the sort of deviations we'd see that turned out completely correctly. While certainly if you could just plop dark matter anywhere you wanted and hold it 'stationary' you could overfit to any data you wanted, the models that work have dark matter right alongside regular matter, driven by the same forces. The only reason its possible to derive such models at all is that galaxies behave so much like there's more 'stuff' there that we just have to fill in the blanks. Brute forcing a dark matter solution to a world driven by MOND would be at best a feat, and more likely close to impossible. Total side note, I was snooping in your profile and saw that you wrote Zigler. I actually just today tried it out, funny coincidence no?