I think you are incorrectly missing that many larger units (both 3+ bedroom apartments and houses) are currently filled with singles or couples with roommates who would rather live alone in 1 or 2 bedrooms, but can't due to inadequate supply.

Building 1/2 bedrooms would help those people move out, freeing up larger units for families.

> I fear it's just going to enrich the property management class

The property management class benefits most from the current system with no construction and high rents. Building a bunch of 1/2 bedrooms, triggering lower rents, would cause them to lose money.