Not all ancient societies sealed themselves off from everyone else, but because the world wasn't a global village back then, the geographical separation entailed independent cultural evolutions in practice for the larger civilizations. When they did come into contact, they'd often try to conquer and absorb each other. The Roman Empire was somewhat exceptional in allowing its conquered peoples to practice their religions.
Not sure what you're on about with your second point. Ancient societies passed on mainly secular goods like skepticism and atheism? Of course the ancients developed their societies in concrete, infrastructural ways, with technological inventions, for example, some of which have been passed on. And some societies were more theistic than others. Theism is more important to Western monotheists than to Eastern mystics and pantheists or to Chinese pragmatists.
Yet how does any of this affect what I say in the article about interfaith dialogue in the shadow of secularism? Are you saying religions have always operated in that shadow? Not so for theocracies, alas. That's why there's not much secular progress today in places like North Korea or Saudi Arabia.