We use university degrees and GPAs as a proxy for IQ, and even with grade inflation, it think it is still a good proxy.
And IQ also has a correlation with social status, like it or not.
> between "qualified" candidates
I'm presenting from the point of view of the hiring institution. But still... If I were a law firm, I wouldn't hire a lawyer who hadn't gone to law school. Why would we behave differently with software engineers?
That same guild has coordinated a test & accreditation process that largely spans their industry.
Whether or not this process has led to better lawyers or legal procedures is an open question, but the software industry has no such standardization, testing, or work embargo, so they are largely not comparable.