What do oil and gas exports have  to do with the so-called decimation of the middle class?

Presumably you are blaming the oil and gas industry for the hollowing out of Ontario's branch plant manufacturing industry. Yeah, that's what caused it all right.

I guess the answer is clear: kill the oil and gas industry and soon it will be like 1964  all over again in Ontario, churning out branch plant  trucks, TV's, tires and tampons, plus actual Canadian controlled  maple syrup bon-bons,  to an eagerly awaiting world.