If the market is adequately regulated they wont be shittier landlords. There somehow is this romantic idea of smaller scale landlords to be like the good old guy that want to help a family find a good place and accept a modest profit. They exist, but the majority are just equally cutthroat like large corpos. Difference is that large corps have more means to be strategic about it and accept risks like 5% of tenants suing successfully while the rest just accepts the illegal treatment.
It is not an argument against regulation though. Regulation of markets like housing and healthcare, is reasonable and necessary. These cannot work as free markets because the one side has their life depending on it, wheras the other just can have another customer.
living isn't a requirement, have you seen how many people willingly consume drugs and sugar despite knowing the risks. Let the free market collapse the upper class (almost certainly after the working class but still)