Image capture from LinkedIn here.

Market rate housing needs an ROI or capital can't lend

Value being greater than cost is a good thing, actually. And, not just in housing and even through time.

At Present, constrained supply guarantees projects get built because high demand means a reliable market

restricting supply guarantees fewer projects get built because that is exactly what restricting supply means.

Affordable housing offers no returns (and are often negative)

Because the operation of the supply restrictions are precisely through limiting affordability by making it illegal or requiring more costs. Or, by alternative definition of affordable - subsidized, that is also inherent in the name subsidized. While in the absence of supply restrictions less subsidized housing would be needed there will always be people who could use help.

how do we reckon these opposing truths?

There are no oppossing truths here unless you are confusing yourself by trying to be too clever by half.