It also ignores corporate cultures.
Backend engineering for a web startup is very different to backend engineering for a Wall St HFT house. I wouldn't expect someone who worked in one to be expert in the other.
Even within the web startup world, fullstack with MEAN is very different to fullstack with PHP/Apache/MySQL - not just technically, but culturally.
So I think what you have is one of those toy models that management love so much.
I'd like to see some hard big-sample-size evidence that it really does improve hiring outcomes in practice.