The overlap in the long term and promo fares means the most expensive economy fares (typically Y class) will always be more expensive than the cheapest A class PE promo fares, and typically priced around the same as E class PE fare.
I was looking at flights to the US the other week and during school holidays the difference between economy and PE was only $200 as discounted A class PE was available but there were no economy specials due to school holidays.