Have you read the book Moneyball? It offers good insight into how professional athletes are evaluated and rated by executives, coaches, and other so-called experts. In the end, the process they use for evaluating athletes is highly subjective and based largely on stereotypes, peer pressure, and tradition.
It is an oversimplified process, and despite the fact that there is very little actual analysis, the people making these evaluations take great pride in what they do and in the opinions that they form.
They were wrong about Goff for many, obvious reasons; some have even admitted it, but most, for the sake of preserving their reputations and standing among the public and their peers, feel the need to be right at any expense so their old opinions persist despite better data, or better ways of analyzing the same data, being available.
The thinking about Jared Goff is a product of this.