But it is how the size is gained that matters most. Adding in a third row, but over all height and width are the same, not so much an improvement as the third row restricts airflow and has hotter air flowing across it. Themodynamics show that the biggest factor in heat transfer is the difference between the heated medium and the cooling medium, the larger the differences the greater the effect. Now if you were to take a two core radiator and lengthen it enough to add in the same amount of tubes a three row gave you then you'd see a larger increase in cooling than the same tubes in a three row configuration. Which is not to say you don't get some increase in cooling with a three row, it's just a diminishing return in that style packaging.
Lots of mopars had wider radiators in a HD cooling package. 22 vs 26" radiators come to mind. However, if you don;t hae the room, or don;t want to cut up the core support, then you are limited to what can fit there and in that case a three row is an improvement, of sorts.
Of course there are other factors too, such as fin count. More fins per inch of tube length is better,, until it gets dense enough to restrict airflow. To overcome that, to an extent, you make wider tubes that allow more fin to tube contact. That is limited by materials strength though, Aluminum tubes can be wider than brass in this case, but brass conducts heat better, however the lead based solder that connect the fins to the tube, in brass applications, negates that to an extent. Aluminum tubes and fins are welded, all aluminum, so no lead restricting heat flow.
Many variables