“The lay down seat should in all sprint karting classes be faster”
Its just the opposite. Go to a road race and watch the laydown karts crawl through the corners compared to the “sit up high” drivers.
“I shouldn’t have to explain but because you do not have a differential you “MUST” unload or slip the inside rear.”
“And it is fact the same grip distributed across two rear tires will go around the track more efficiently or ‘freer’, then with increased unloading of the inside tire and more use of the outside tire.”
You kind of answered your own question. You are correct, you must unload/slip the inside rear tire. If you ran a laydown style seat that increased the weight on the inside rear, the kart wouldn’t rotate as well. Plus, with the laydown seat you would decrease the weight transferred to the outside tires through the corner resulting in less grip/slower corner speed.