I agree it should stay as place=suburb. No matter how much certain mayors like to call their municipalities "cities", they are an integral part of the Athens metropolitan area, not distinct settlements in their own right. Statistical settlements are helpful, but should not be the basis for OSM classification. In the countryside, the reverse problem is visible (named settlements that have been absorbed into others due to population loss, and are no longer statistically named as settlements even though locally they are regarded as such.)