I don't see how anybody can deny that thicker is better based on these manuals. We see 20 weights being defended often as "well the manufacturer knows best", but that's really not the whole story, because the manufacturer recommends 30 weight when they don't have their hands tied to maximize fuel economy tests for every last percentage point.
To me, that says the manufacturer doesn't recommend 20 weight, but the hoops they have to jump through do. Without CAFE tests, it seems we'd be steered into running 30 weights like elsewhere in the world, and like thinner oils are a calculated decision to reduce engine wear by "enough" but not as well as possible.
Based on opinion and emotion.