Well,
Like electricity, the higher the voltage between two locations the more electrons will flow, just as in the BTUs flowing from hotter to cooler. Add in that oil tends to form up around the cooling tubes in a cooler and insulate the hotter oil from those tubes. Thus great lengths to cause turbulance in the oil tubes to scrub cooler oil off of the tubes and improve heat transfer.

In the case of transfer of heat to water vice air, then water wins the race every time. So an oil to water exchanger can be very much smaller than an oil to air exchanger of the same BTU capacity.

So transfering the oils heat into the coolant is far easyier than removing it from the coolant into the air.
So, coolant and oil temps will be very close to each other. You will notice that oil temps in rotaries tend to track the throttle setting,  and are best kept below 180 degrees for good power. Best power will be found well below 160 degrees of oil temp, but very difficult without a very large water radiator. The oil temp is an indication of rotor face temps, and higher temps mean lower cylinder filling, and thus lower power output.

It is difficult to over cool the coolant, as the engine run fine below 160 degrees of coolant temp.

Other advantages include no scat tube to a cooler is required. Actual location is not important. Smaller size than for the oil to air cooler. And very good oil temp control, and thus more power.

NASCAR uses them, but their coolant radiators are huge with 4 or 5 rows of tubes and the cost of a used car.

About 70% of the BTUs going into the engine escape as waste heat. Most as exhaust gas temperature. The rest through the coolers, and into your shoes.

Lynn E. Hanover