The Sin war supposedly took place approx 3000 years before the current events of the Diablo series according to the Diablo 3 wiki.
How does Leah even know what Pre Sin war Architecture look like?
Was this just more sensationalist, melodramatic, largely irrelevant nonsense that the lazy Diablo writers had their characters spout in order to produce a sense of "awe" from their players?
If that was the case, they failed. Miserably. I just felt embarrassed for the voice actor who had to say that line. It was embarrassing Blizz.