Everyone is correct. The main problem with looking at on time performance is each airline use a different criteria to determine when the aircraft has arrived so when you look at the numbers, you are not comparing apples to apples.

Airlines use one of the following to log the arrival of their flight:
1)Parking brake set.
2)Main cabin door is opened.
3)Main engines turned off.

There might be others. . .

Even within the same airline company you can have differences. American Eagle FA's get upset when the ground crew is worked by AA mainline. Eagle crews go off the clock once the main door is opened but the ground crew do not want the passengers getting off until they have off loaded all of the checked carry on. I have heard fights between the two when the ground agent tells the FA to keep the passengers on board.