There is probably a correlation between top-tier CS pedigree and performance, but using it as a filter for joining a startup is detrimental. The chance you're missing a "diamond in the rough" is high, and those are exactly the folks you want.
If you're Google and have tons of résumés to sort, then fine; but in this case it seems a good way to miss a great hire.
It is elitist, but also their choice, and while the false negative rate may be high the false positives are what they are worried about.
I personally filter on "has made major contributions to interesting projects" and "speaks two or more human languages". That discriminates against a lot of people too. My tertiary filter is "ignores my filters but is impressive enough anyway".
If you're Google and have tons of résumés to sort, then fine; but in this case it seems a good way to miss a great hire.