I don't understand this thread, lol. Do you guys read the ability descriptions in-game?
(from heroic) "As long as this unit isn't Toppled, it has +50% Tenacity"
Which means...before hitting the door, and after it goes back up again, he has +50% Tenacity. But while the door is DOWN, he doesn't get the bonus tenacity and is therefore easier to land debuffs on. So why is it surprising that it's harder to land debuffs after the door goes back up?
Personally I don't even bother trying to land speed down before dropping the door on him...when I do heroic P2 my first 2 toons to act will kill the control panel. Phasma is my leader and is third to act, so I pretty much always get it that my first action after dropping the door is Fusillade, which is easy to land speed down with (and mine isn't omega'd) once the rancor is toppled. I rarely have to restart because speed down didn't stick.