Here's my thoughts:
1. The commenter is correct that ACKS is based on assumptions of labor productivity, food price, and so on, that are based in the historical pre-industrial world. To the extent that a campaign setting widely varies from the historical pre-industrial world, ACKS needs to be modified.
2. Whether you use ACKS or another system, if you want the trade/realm type rules we offer, you will have to answer basic questions like "how much money does a peasant earn" "what items are available in a city" and "how much does a horse cost". f you want the setting to be coherent, you have to make assumptions and build from them. The virtue of starting with ACKS is that you are starting from a functioning set of assumptions and can tweak them. If you start with other systems, they are generally less coherent.
3. The problem with "An Echo Resounding" lies at the interface between its realm mechanics and the underlying game's mechanics. For instance, if you find a dragon hoard, and want to convert that into "+4 Wealth" the system doesn't provide a clear interface to do so. It's left to the Judge to decide. The reason ACKS is built on a hardcore set of assumptions is specifically to be able to answer questions like "how much is a dragon's hoard worth relative to the income of the local duke".
4. The assumptions in ACKS are probably more robust than the commenter suggests. If your standard is the rate of change of the modern era, the most surprising thing about human history 10,000 BC - to 1400 AD is how slow the progress of technology is. ACKS can model 1000 BC, 0 BC, and 1000 AD with respectable efficacy. As long as your "Dark Sun"-ish world is closer to a pre-industrial world, ACKS will work well. I think ACKS would have more trouble with, e.g. Eberron.