Dunkelzahn's death was just like pretty much everything in the Sixth World. Nothing is simple. There are always layers behind layers that the common people (even those who are fairly high up or far in) will never see. There are some people who whine about anything to do with Earthdawn or the Enemy. However, pretty much every magic-based adventure or plot point relates back to the Fourth World or earlier in some way. Bugs? They were already present in the 4th world, and the Powers That Be regard them as precursors to the Enemy arriving. The Infected? They existed, in one form or another, during the last cycle, and popped up even before the Awakening, in some cases. Some even slept from one age to the next. Artifacts and lost magics? Goes without saying. Dragons and Immortal Elves? These are only the most flagrant things from the past ages of magic, and so people focus their hate and vitriol there.
Dragons are scary creatures, and Great Dragons more so. An adult dragon can be killed. It isn't easy, but it can happen. A Great Dragon is all but impossible to bring down. But it is possible. However, it takes a massive undertaking, not unlike stopping a hurricane from spinning. Could mortal metahumans accomplish it? Perhaps, given sufficient numbers and resources. But it is not something one should consider lightly.