Who told you or where did you read that there would be a performance gain going tubeless on road bike? If someone told you that or if you read it somewhere....they are wrong.
You will see a gain on a mountain bike in the performance category Being that the tires and tubes are larger you will have a decrease in wheel weight and when going over uneven terrain, where the tire gets deformed a lot, the there isn't a friction fight between the tube and the tire.