The paper addresses this. Rather than (futilely) attempt to nail down the "one true electorate", the paper defines an infinite family of comparators, depending on a hyperparameter which is, essentially, the choice of which environments get to vote and how to count their votes. Crucially, this doesn't change the truth of the structural theorems (except that some of the theorems require the hyperparameter satisfy certain constraints).

Indeed, any attempt to come up with "one true comparison of intelligence" (as opposed to a parametrized family) should be viewed with skepticism, because it really must depend on a lot of arbitrary choices.