It's not a free market though, landlords got in when supply was higher than demand and then restricted new development through zoning laws, red tape, and environmental lawsuits to ensure that rents remain high.

Plus, landlords that are out of state actively drain the local economy. If we really want an optimal and free market, every bit of Boston should be rezoned to increase density. You don't need another seaport, build more Back Bay/Fenway/South End style neighborhoods (the most desirable parts of Boston) and everyone will be happy.

Landlords that reside out of state should be taxed at higher rates to encourage local ownership (and local recirculation of rent money). Corporate ownership should be taxed higher than individual landlords, with an increasing tax rate dependent on how many units you own. Renting a retail property to a chain or bank should have higher tax rates than local businesses. Triple deckers without historical significance should be able to be replaced with 5-6 story mixed use brick buildings (built to the property line with a setback in front) without any hassle.

There's so many pen stroke changes that the city could make to make the market freer and benefit local residents at the same time.

Landlords set prices as they see fit, but they only have buyers at such high prices because of shitty laws and regulatory capture. And it's not like they're locals, a lot of these landlords are from out of state investors or corporations.