I think Eliezer wrote this in part to answer your kind of argument. In short, aside from your first scenario (which is very unlikely since the probability of an asteroid coming to destroy Earth is already very small, and then the probability of a narrow AI making a difference is even smaller) none of the others constitute a scenario where a narrow AI provides a permanent astronomical benefit, to counterbalance the irreversible astronomical damage that would be caused by an unaligned AGI.
I think Eliezer wrote this in part to answer your kind of argument. In short, aside from your first scenario (which is very unlikely since the probability of an asteroid coming to destroy Earth is already very small, and then the probability of a narrow AI making a difference is even smaller) none of the others constitute a scenario where a narrow AI provides a permanent astronomical benefit, to counterbalance the irreversible astronomical damage that would be caused by an unaligned AGI.