Building any housing (even just exclusively luxury units for rich people) over time decreases housing costs across the board. This has been studied and is a verifiable fact. (This right here is all you’ll see on Reddit though, that’s like the defacto answer, no nuance, hence the downvotes) However the other side of the coin is that this takes time to even out so only building luxury housing will short term cause a homeless problem that might not be rectified even after the market balances itself
Quite literally in the same paragraph “nonetheless, the neighborhood level benefits of market rate development are promising and indicate an important role for both market and non market solutions to the housing crisis” then we can go to the other studies grouped into this review and we find that 5/6 papers grouped together show market rate units lower overall prices. Learn to read a whole research piece
So when you actually read an entire research piece and not a tag line you actually understand the context of “not endorsing” market rate units. They’re not arguing that market rate units don’t lower overall rents and increase affordability. They are saying it’s not the only end all solution, it can and should be used to compliment other solutions