There has been change in how Central Asia is viewed over time. For example, the Central Asian contribution to Medieval science is often invisible, being lumped in as just part of "Arab science" or "Islamic science". "Arabic science", as in "science written in Arabic", is a better term than either of the former (which also hide much of the contribution from Jewish and Christian writers). Some newer works are more careful, and even discuss the older roots of Central Asian/Persian science, integrating ideas from India and Mesopotamia (and the West) with their own. On a larger scale, outside science, Central Asia can disappear as just part of the Islamic world which is so obviously (from the Western perspective) centred on Baghdad, or even Egypt and Damascus.

However, key Central Asian cities such as Merv, Balkh, Bokhara, Samarkand, etc. have long been famous for their wealth and size, and for being important trading centres, at least before the carving up of Central Asia by Russia and China. For example, Rawlinson notes the importance of Balkh (Bactra) and Merv, and the prosperity of their surrounding areas. They can be less prominent in Western histories from Western Europe, especially older ones, due to their greater distance from the West. Just consider the relative invisibility of Byzantium in such histories, which often exists merely to be sacked during the 4th Crusade and then conquered by the Ottomans.

Rawlinson's Chorasmia appears to be the western 2/3 of modern Turkmenistan, largely the desert region between the Amu Darya (Oxus), Caspian Sea, and the mountains of northern Iran. His description is quite reasonable for this region. For other writers, Chorasmian/Khwarazm includes lower Transoxiana, and others include upper Transoxiana, Margiana, and Bactra. At the extreme, "Khwarazm" is sometimes used to mean the entire Khwarazmian Empire at its largest, approximately all of modern Uzbekistan, Turkmenistan, and Iran, and a substantial part of Afghanistan.

So, for your specific point about Chorasmia, it depends very much on which Chorasmia/Khwarazm is being written about. Rawlinson discusses the smallest of these Chorasmias. His Chorasmia is today largely desert which cannot be accused of great agricultural productivity, and has been such desert for a long time. Rawlinson's Parthian Empire didn't include the great cities of Transoxiana, so they aren't mentioned. Those just to the south, Merv and Balkh, the centres of Margiana and Bactra, appear in his book, but these were the borderlands of the Parthian Empire, and he doesn't go north.

That said, while the large cities of Central Asia were large and were important trading centres, they were much smaller than the Ancient/Medieval mega-cites like Rome, Baghdad, Hangzhou, Kaifeng, Beijing. The largest only reached populations of about 100,000, and the smaller ones were probably only about 20-30,000. Baghdad at its peak population may have had more residents than the 20 largest cities in Central Asia combined.

Reference:

Chandler, T., & Fox, G. (1974). 3000 years of urban growth (Studies in population). New York: Academic Press.