Earliest proof of cooking shows our ancestors liked well-done fish

They did not have a crockpot, Mexican dig a pit and bury a whole hog in coal and let it cook Google Underground Smoked Pig

Deep fried fish will beat sushi on any day

No proof needed, one can think about it and then it’s obvious. Most if not even all such knowledge or actions come from try and error. Then , once upon a time in those small fishing tribes, one sib ate the raw fish as it was and everyone died, the second sib first threw it into fire , but the fish burnt away, wasn’t delicious etc, they mostly died from hunger or disease too, until they only held it into fire and bbq-ed it , but the other , the third sib cooked it and didn’t die. Well, yes, they first didn’t really cook it, of course not, but it fell into a hot spring by accident, but as it was something difficult to hunt and too precious to let getting wasted one tried to take the fish out of the spring and sacrificed himself by dying later too from high temperature and burns , but the rest of the second sib had now delicious fish and such the cookers and bbq-ers happily survived and made also your and my existence possible.