It seems significant that the lens galaxy has little dark matter, in light of the recent discovery that DM seems not to be needed to account for rotation curves.

If DM is still needed to account for galaxy-cluster lensing, would that suggest DM is much more diffuse than hadronic matter? Would that imply low-mass DM particles, or much more slowly-cooling DM, something else, or indeterminate?

Am I misremembering, or had normal low-mass DM particles already been ruled out? How is DM supposed to cool, anyway?

TIA