It is already the case - go try and pursue a career in academia and see how much money you make compared to a plumber.
Some not-very-intellectual jobs (plumbers are everyone's favourite example, which makes me suspect there aren't many others) pay pretty well. But most don't.
Some jobs that usually pay pretty well: Software developer. Lawyer. Doctor. Quant. Corporate executive.
Some jobs that usually pay pretty badly: Cleaner. Waiter. Shop-floor sales person. Bank cashier.
I think these are more representative than comparing adjunct professors with plumbers.
It's hard to disentangle the effects, since many of my age peers who went the blue-collar route weren't exactly responsible... but those who were, and some who weren't, still did very well for themselves. Theoretically, maybe we white-collar workers would do better after 20 years - but not if our blue-collar friends invested their savings in the meantime (which many do).