At operating temp the radiator cooler only cools the trans fluid to the engine coolant temp. Say you have a 195° t-stat, after the antifreeze flows out and down through the radiator. The temp drops what, 30°? So 170°?
The small OE auxiliary cooler might take the temp down another 20°? I'm pretty sure that the transmission doesnt operate all that well under 150°
So here's the litmus test. If you remove the OE radiator cooler, replace the OE auxiliary cooler and run one efficient large size cooler, and a temp sensor, that will cool the fluid to the 160-170 range when you're loaded and towing, then I'd agree with the previous owners cooler reengineering.
I guess if it works, dont fix it.