It's been a bit since I saw the cutscenes but IIRC it was less the Ancients couldn't interact with dynamis at all or manipulate it but that it made their creation magics go out of whack and become uncontrollable. Their society relied heavily on these creation magics so any response to Meteion would involve utilizing them. I'm not sure how they could have mounted a proper offense with the tools they had available assuming they could reach her. We as the WoL don't have pesky creation magics to fall out of our control.