A simple question about the signaling model of education

Let’s say, for purposes of argument, that education is 100% signaling, and furthermore let’s assume that the underlying traits of IQ, conscientiousness, and so on are not changing in the population over the relevant period of time.

Now consider a situation where income inequality is rising, at least in the early years of jobs.  Since employers cannot discern worker quality — other than by observing the signal that is — this should imply that getting an education is “more separating” than it used to be.

That in turn has to mean that an education is more rigorous than it used to be.  No, not “getting in” (employers could hire their own admissions officers), I mean getting through.  Finishing successfully is more of a mark of quality than it used to be, because finishing is harder.  Finishing is harder because there is more rigor.

Is this true?