If you really care about rental affordability, you should really care about building as many new apartments as possible. Econ 101 is playing out right now in the U.S. apartment market: It's all about supply and demand. 

Build MORE, rents grow LESS. 

Build LESS, rents grow MORE. 
Check out the data showing rent change based on volume of new supply. There's a clear correlation between SUPPLY LEVEL and RENT GROWTH right now. 
 

Submarkets expanding their apartment stock >10% cut rents nearly 2%. 

Submarkets adding 5-10% more units cut rents by about 0.5%.
 

On the other end, submarkets that added <1% new units INCREASED rents nearly 3%. 
To be fair: Rents don't always fall when supply is added -- particularly when supply fails to keep up with high demand. But there's no doubt rent growth is more limited than it'd otherwise be absent supply. 

We expect these trends to widen over the next 18 months as apartment supply nationally hits multi-decade highs... but supply isn't evenly distributed, and neither will rent cuts/growth.

 It's all about supply. Build, build, build.

." Announces in his statement Jay Parsons - Rental housing economist