Question from a non-airline-type...
Wouldn't the "thinning out the stack" theory really only work up to a point?
If an airline (or whatever company) sets a minimum standard, then all those with the minimum standard get a look-in in the selection process. So, with QF for example, they do not require a degree, so everybody with the minimum qualifications gets looked at, including those without a degree. Then it comes down to flying experience and testing performance.
I suppose what I am trying to say is that you can be a PhD in Astrobloodyphysics, but this gives you no greater advantage of being looked at than someone satisfying the minimum educational qualifications. The significance of qualifications may come into effect if you are marginal in the testing and are avoiding being dropped off the bottom of the list.