Wing Chun vs and Untrained opponent? (I don't do Wing Chun I practice a Long Fist called Pigua Quan... but I have a good friend that has studied the art for twenty years, I've sparred with him too many times to count)

IMO... Wing Chun is a very good art against an untrained opponent (some arts IMO are not) Most untrained opponents stand in the pocket swing away while giving their center line up. IMO this sounds like "Candy Land" to a practitioner of Wing Chun.