In OP's parlance, a shit job is an exploitative job.

He is saying that through progress there are fewer "shit" jobs, so there are fewer people exploited.

It never has been and never will be economically viable to pay a ditch digger the same amount as a doctor. So as long as jobs like ditch-digging exists, people must be "exploited" to fill them.

I don't think this meets specification. "it never has been and never will be economically viable" scans as handwavy, and I've yet to see anyone calling for "ditch diggers" (job automated out of existence by heavy equipment several decades ago, btw) a wage equivalent to what an MD makes. Your assertion, in essence, appears to be that people get paid low wages because low wage jobs exist. That does nothing to explain why a job sufficiently important to require a human being to perform is low-paying and so far nobody has advanced an explanation that takes into account historic levels of corporate profits and income inequality while wages have been basically stagnant since the 70s.

I think what the parent post is saying is that exploitative labour practices enable the existence of elites with enough leisure time to create philosophical and technological progress. It's basically the argument that there would be no great classical civilization without slavery, so slavery is justified by the achievements of the civilizations that used it.

I would like to think that in the 21st century we could have idleness for many, and abusive exploitation for none.