[AnthonyMouse]

> Surely 20 units on a single lot will be cheaper than the single family house.

Those units will cost less -- largely because at scale they're resulting in more housing supply -- but the detached houses will decline in value in terms of housing but increase in value in terms of land because you can now build more on the lot.

> saying “downzoning good, actually” because a developer might pay more?

The argument is the opposite. Downzoning is bad -- even for existing homeowners -- because a developer would otherwise pay them more for their land than they'd be losing in the value of their house.