the problem with this logic is that a 1.9 million pound oil rig with 200,000 pounds of downforce, drilling 17k ft deep into the earth, being completely lofted, suspended mid air, and rolled, is a much more certain example of EF5 damage. the parking stops in greenfield have plenty of variables and factors that could impact the windspeeds required to do the damage. as june first says, the calculations are in idealised scenarios that might not be accurate to real life. there is no world in which anything other than a EF5 tornado does the damage seen at the cactus drilling rig, where as there is a world in which winds lower than the EF5 threshold perform the damage to the parking stops seen in greenfield.
also, surveyours have said that some of the damage to homes in piedmont, such as the trenched home, are "undeniable EF5 intensity", language i've never really heard said about any other tornado, langauge that shows how confident they were about its intensity. if piedmont didnt hit cactus, im fairly confident that some of the damage to homes wouldve been bumped up an extra 5mph so that the tornado receives and EF5 rating regardless. i dont really see a world in which piedmont doesnt get an EF5 rating