Some intellectually satisfying jobs (academic, author, artist, ...) pay badly. But many others are well paid, and probably most of the best-paid jobs are (1) largely brainwork and (2) pretty interesting to do.

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.