[scythe]

>but no matter how much you weaken zoning protections to get there they somehow never manage to swing prices when demand, like it is now, is just so much greater.

It doesn't make sense that they would, but that's okay because it's not the goal. In oversimplified microeconomic terms, new housing is built for the current price point, and can have the effect of preventing a price rise -- preventing demand from exceeding supply. Prices come down when supply overgrows demand, which doesn't happen by increasing supply, because the people doing so would lose money: demand has to decrease. tl;dr: high prices cause construction, but it's a negative feedback loop.

Concerns about housing quality seem misplaced. In a large majority of cases, new housing tends to be better than old housing, thanks to innovations in construction. High rises were popular in the '70s, which is why low-quality high rises are common: they're old.