When Manse Everard is in the Carthaginian timeline, he regrets that Dante and Shakespeare do not exist. Would the alternative timeline eventually have generated literature as great as that of Dante or of Shakespeare? Possibly but not necessarily. Anderson's point is that, in that timeline, there had been neither science nor social progress by the equivalent of our year 1960. The point is made even more starkly in "The House of Sorrows" and in the concluding section of The Shield Of Time. History might never have broken out of the cycle of slave-owning empires collapsing into dark ages from which nothing ever emerges but another slave-owning society.
In "Delenda Est" and "The House of Sorrows," no monotheism means no science. In The Shield Of Time, papal victory over the medieval emperors means a theocracy that prevents either freedom or science. How probable was our history? And how safe is our present civilization?