I'm not familiar with recent Persian archeological findings, but some of the quoted death tolls for Mongol invasions would have required a) that the city had an unrealistically high population for the time period and b) would have deserted the city, when later records indicate the city was still functioning (sometimes because it rebelled again). The archaeology also supports many of the cities in central Asia not being abandoned as a result of mongol attack & occupation.

To take an example, the massacre at Merv was claimed at 1.3 million people, at time when the largest cities in the world probably had 300,000 people. Yet somehow it revolted again 10 months later (the alleged massacre happened in February 1221, it revolted in November 1221).

From John Man, The Mongol Empire