> it doesn't matter if prices are falling or rising, it only matters how the ROI of building compares to other investment opportunities

Correct, which it basically doesn't in Austin, which is why construction is decelerating.

> we can also make it cheaper to build

Yep, this is the only structural solution. The "just add supply" runs into the problem of price equilibriums. The reality is the input costs of building housing basically guarantees that housing is hard-to-attain for any local market. We need to address the cost of inputs. Temporary reductions in price are temporary and the market will self-correct back to restrict supply (as we're seeing in Austin) until prices go back up to being hard-to-attain.