You don’t need your own estimates to call BS on theirs. Including simply on the premise of the volume of the universe, most of the universe is an empty void. Even if you allow somehow for the traversal of intergalactic void in your local clusters this alone should put a much more serious dampening effect on the expansion of any given species.

It also assumes that species can even get to the technological level required for galactic and then intergalactic expansion and maintain that level pretty much indefinitely.

But then again this isn’t a research paper or even a particularly serious statement.