I don't follow, If Petty grew up in this era he certainly had the talent to win. Now if you wont to drop a 40 year old Petty in a Gen 7 of course he would struggle. If you dropped Kyle Larson in a 1975 Matador he would struggle also
I agree that Petty had a decided advantage over everyone due to factory backed cars that no one else had in the beginning but if he came up in this era I believe he could have won a few,he wasn't a hack by any means.