However likely they are, I expect intelligence explosions to be evenly distributed through space and time. If 100 years from now Earth loses by a hair, there are still plenty of folks around the universe who will win or have won by a hair. They'll make whatever use of the 80 billion galaxies that they can--will they be wasting them?

If Earth wins by a hair, or by a lot, we'll be competing with those folks. This also significantly reduces the opportunity cost Roko was referring to.