Are you grasping the astronomical spacial and historical scales involved in a statement such as "... takes over the entire lightcone preventing any interesting life from ever arising anywhere"?

That scenario is based on the idea of life only arising once. A superintelligence bent on short-term paperclip production would probably be handicapped by its pretty twisted utility function - and would most likely fail in competition with any other alien race.

Such a superintelligence would still want to conquer the galaxy, though. One thing it wouldn't be is boring.