This seems like a very nicely detailed response to OPs question. Thanks! Your response brought up some questions and remarks from myself. > DM can be falsified

This seems like a very nicely detailed response to OPs question. Thanks! Your response brought up some questions and remarks from myself. > DM can be falsified perfectly well. I recall hearing that DM was attempted to be falsified based on gravitational lensing. Is that correct? > If DM interacts purely gravitationally, then yes, considering it either matter or an artifact of space-time is merely a matter of preference. Simply move the DM part of the energy-stress tensor on the other side of the Einstein equation. Would DM as matter not have inertia, whereas treating it like an artifact of space-time would leave it without inertia? > Differentiating it from MoND or similar theories will then be based purely on how well the theory fits. A simple question here would be: do all galaxies of similar size have the same amount of dark matter. If so, then the uniformity of dark-matter would need explanation. If not, then I think something like MoND would have a hard time explaining why these similar galaxies rotate at different speeds.