Depends on both how you draw the line and the particular engine.

I looked at at this some time ago and decided I a 356 was mainly air cooled. Most of the heat is rejected directly from the cylinder head or the cylinder barrels, and most of that heat gets into those parts without ever going through oil. The head, cylinders and valves are in direct contact with hot combustion gasses, and all conduct the majority of the heat they absorb directly through metal to cooling fins where air carries it away (the valves shed most of their heat to the head through the valve seat). The pistons shed most of their heat through conduction to the cylinders, and while some of that is through an oil film the majority does not require the oil to be there.

As an air cooled engine increases in power, however, more and more features are added that increase the percentage of energy going through oil. Piston squirters spraying the bottom of piston, additional oil passages lubricating the cam, etc, all contribute to both cooling specific hotspots and sucking away more heat in general. In the extreme you get to strategically placed passages going through the head that focus on cooling the area between the valves, and done correctly this can even allow 4 valve heads without water cooling (google the BMW motorcycle “oilhead” for some modern examples of highly oil cooled heads). These tricks are increasingly required as an engine increases in power output, and in very high power examples can lead to over half the thermal energy leaving the engine through the oil and then oil cooler.

Over 50% through the oil is far from the norm, however, even in highly modified air cooled cars. One simply needs to look at the size and surface area of the oil cooler and realize that it’s not running as hot as the cylinders/ heads to understand that it can’t reject the majority of the heat in most cases. One can also calculate using the capacity of the oil pump and oil temperature before and after the cooler to arrive at similar numbers. There are some grey areas- does heat rejected from the valve stem to the valve guide (through an oil film) count towards the oil cooled total? Even counting this energy, however, every remotely stock 356 engine is far more air than oil cooled.

I think “partially oil cooled” is correct, and the oil cooling is required for the engine to run. However I can’t agree with “primarily oil cooled” on the basis that most of the energy does not go through the oil.