The big catch is that some of the signals are abstract and built on non-public data. And as Google puts more weight on things aligned with "brand" you can know

The big catch is that some of the signals are abstract and built on non-public data. And as Google puts more weight on things aligned with "brand" you can know that they are doing so, but that still doesn't solve the problem of needing to build brand. IMHO we are starting to move to the point of SEO where we are moving away from knowing the data to understanding deeper marketing functions that create the relevancy signals as a side effect. If you have a higher visitor value than your competition and can afford to buy more ads than any competitor can then reinvesting those profits at some point creates a winner take most market segment where you get a lot of the relevancy signals built as a free side effect of buying tons of ads.