You're suggesting that there are no such things as conceptual properties. You are wrong. Calling set_area should conceptually set the area of whatever object it is. And that "area" that is being set is a thing, which (in OO programming) means you implement it as an object.

Furthermore, the Area->set method of a sub-object can do absolutely anything the set_area property can do. It is every bit as abstract, it just corresponds better to the suggested model. Notice that in my example, both Area and Radius operate on the radius value. They do not have their own independent set of data; the radius value is owned by the Circle object.