What you ask is answered by the tremendous high cost of SEO: tremendously high because obtaining one link does not do that much long term, thus the whole strategy has to be longer in approach and keep targeting only the highest scores. These can be “poor minnows” even btw.
Just like PR UA always has always more data (if I understand it correctly) and thus becomes always fairer in output value with each new data input.
Nope, it is possible to attack UA, so to state that "more data always becomes fairer" is a bridge too far. However, we're virtually simulating severe attack scenarios to UA, and harden UA against it.