In fairness, I think many physics students assumed that someone had done the GR to show that DM wasn't just a GR effect. I recall a near identical situation as

In fairness, I think many physics students assumed that someone had done the GR to show that DM wasn't just a GR effect. I recall a near identical situation as the author when it came to someone presenting galaxy rotation curves based on newtonian gravity and thinking "that's odd, but someone has surely done the math by now".