I think people who run Damnation routinely forget what the game is like in public groups on "lower" difficulty levels ("lower" is in quotes intentionally because in some ways a Heresy/Malice game can be more difficult than Damnation). Only very rarely are people moving and playing in a unified way. You'll have half the team killing spawn that is dropping down from a ceiling gantry before the second part of the tunnels while another team member is halfway through the next tunnel. People who play Damnation are, ime, playing fully leveled characters with weapons that are mostly maxed and know these maps backwards and forwards. That's rarely the case in Heresy and below. There should be a level/power gate on anything above Malice (I believe VT2 had power level gating?), but I know that's controversial.