But cars getting better and cheaper shows up as more total cars getting sold, which does show up as increased material usage, at least up to a point.
Yes, I’d just say that there’s a lot resting on that “up to a point”. Lots of goods, cars included,, fairly rapidly saturate in the benefit that they bring, and hence in how much of them get consumed. At least in the US, we’re at the point where there’s almost as many cars as people, and there’s fairly little use to more than one car per person. This puts a pretty hard upper limit on how much increased car production quality/efficiency will show up (and to a lesser extent, has shown up) in material use.
My informal perception is that in the “developed world” at least, a significant proportion of goods are already far enough along in this process that there’s a substantial decay in the quality of their inputs as proxy measures.
Maybe, but cars aren’t the only things we make out of metal, either. I deliberately made the categories as broad as possible while staying objective. Still, I agree there’s an issue here.