Yeah ben but some are better than others. To keeps costs low chinese companies will stick right with the maximum temperature as they can get away with because copper is expensive, and a bigger or coil or better core materials would cost more for a higher efficiency transformer they'll go with a lower effciency one every time if it saves them a dime. Commercial or power company transformers will be close to 95% efficient, that cheap one that overheats at load might be 80 percent or lower, they don't care if they waste your energy, doesn't cost them anything.