Yes. Because both of those have actual data, and are thus useful - your reasoning can be tested against reality.

We just really don't know very much about the roman economy, and are unlikely to find out much more than we currently do. Generalizing from one example isn't good .. science, logic or argument. But it's better than generalizing from the fog of history. Not a lot better - Economics only very barely qualifies as a science on a good day, but Krugman is completely correct to call people out for going in this direction because doing so just outright reduces it to storytelling.