And besides just having "real estate investors" slurping up all housing, people could own one house then rent out parts of it, or a collection of people could own their apartment building together, there are many other ways to make housing work that doesn't involve huge companies owning large parts of the market. A little bit of nuance goes a long way.
It's already a thing, called house hacking. Tough luck if you're a couple that wants a complete unit instead of a room in someone else's house.
> a collection of people could own their apartment building together
That's called a co-op or a condo (the difference is a bit fuzzy to me). This still involves ownership and upkeep of an asset, which many people prefer not to do.
> huge companies owning large parts of the market
Make it publicly-owned, for all I care. Or let it be individual landlords. Or forbid a single company from owning more than 5% of the stock in a city. As long as it's market rate and abundant and competitive, it literally does not matter. More houses = cheaper housing.
> yet the largest landlords in the US was found to engage in price-fixing and artificially raising rents
Your own link shows that we know this happened because there was a Justice Department investigation about the practice. How can you say enforcement isn't happening.