There are many theories of dark matter given at conferences like this. Around that time (2013-2014) I remember hearing about axion theories too. I don't know anything about this person's presentation so I can't say how it displaces the problem of galaxy rotation curves. If the math checks out, I think it would have, but you never know. I would like to see a reaction from cosmologists.

I would hesitate leaning too much on the always part. Fritz Zwicky was the first to notice the anomalous galaxy rotation curves and propose dark matter (is the story that I remember, anyway.) This is probably why it's presented first. It does not mean that it's the most important piece of evidence.

I'm intentionally writing with a light touch here because I don't consider myself an expert in the field.