We are smart enough to know there are limits on what even the most refined software can detect, without human observation. Trust metrics do not measure good or bad to the supernatural extent you have insinuated, they simply do not. If that were the case, badly written pages on big authority sites would deranked or punished to some extent, when in fact that simply doesn't happen.
Also beware of being preoccuppied with 'quality' content to the point where it's no longer BH SEO, but WH SEO being discussed. I see nowhere in your discussion where BH concepts ever enter the equation, such that what the "quality content" mantra ends up being, is an appeal to be more WH. In my book both WH and BH SEO are faulty IM business models, as they revolve around the search engines. More energy should expended on mastering non-SEO based traffic strategies, not deeper chasing of the white rabbit of content.
What we need to be smarter about is avoiding being overly dependent on Google for traffic, hence a de-emphasis on hopping to comply with every algo change would be more helpful. That is a resource and labor-intensive distraction to making bank, whereas pursuing non-SE sources of decent traffic is the way to go for longer term stability of an IM business.