As an aside, Belintar – like the Lunars – wasn’t a practical builder. He build awesome things to magically tie the Holy Country together, but not really practical things for ordinary people. So it is not surprising that Sartar has better roads than the Holy Country or the Lunar Heartlands.
But he Lunars built the Daughter’s Road? The Daughter’s Road is an amazing feat of engineering and magic. But to be honest, it is a military-magical road more than a road for caravans. And it is what was built by Hwarin Dalthippa. No extensions, no new Daughter’s Roads, etc. Great if you are going from Jillaro to Filichet (by way of Mirin’s Cross), or from Cafol to Hilltown (by way of Jillaro). But it does not go into the Heartlands. It does not extend to Alkoth, let alone Glamour.
So like the amazing Fish Roads and Bridges of the Holy Country, it is an awesome thing, but Sartar’s roads are more practical for most people.
Better construction in Sartar? Esrolia had Panaxeles and Sartar brought his masons from the Holy Country’s urban centres. We know there is centuries of architectural tradition in Esrolia.
Panaxles was two thousand years ago. As for comparative urban and rural populations, I recommend looking at pages 173 and 176 of the Guide.