If the conventional was the same in lubrication, then this story about transmissions in low grade autoracing would be false, and I know it isnt. A friend was burning up 3 speed transmissions and could not figure out what to do. He was told to put mobil 1 in it and not only did it not burn up, but he could put his hands on it after a race. Before, it would burn you to touch it. Later, the automakers started using automatic transmission fluid in the manual transmissions. My 93 Ford had it. That is all Dexron is, light synthetic oil.
I agree with what has been posted since my last post. I am no engineer either, but have spent some time reading all I can about the subject. Just weird I guess. IF no oil cooler was desired and synthetic oil reduced temps and it follows that temps are created by friction, then I would guess that solves that question.