You have to restrict investors buying up that newly built housing too.
Homes for people. Not investors.
35% of Americans rent their homes. And they almost invariably rent from investors. Therefore if more than 35% of homes are owned by investors this drives down rent. If less than 35% are owned by investors rent goes up.
It really doesn't matter as long as someone is living in it.
No not really. You just have to restrict the same investor from buying all the housing in an area, and prevent investors from colluding on rents.