I studied the ancient techniques without upgrading the four Dynastys. The efficiency of Tang Dynasty is + 5%, that of Song Dynasty is + 10%, and that of Yuan Dynasty is + 15%.
Then a surprise happened. The efficiency of Ming Dynasty was - 5%. When all dynasties were upgraded, the efficiency of ancient techniques decreased from 20% to about 10%.
Then another round of test was reopened. The order was Ming, song and Yuan Dynasties. It was determined that it had nothing to do with the order of dynasties. The efficiency of four dynasties was indeed lower than that of three dynasties.