There's no precise definition of "luxury" housing.

Any newly built construction is going to cost more than older housing stock. People seem to understand that new cars cost more than used cars, but for whatever reason this understanding doesn't always translate to housing for some reason.

Developers then slap the word "luxury" on the marketing materials to make prospective buyers feel mildly better about spending $800K on a studio apartment. The studio doesn't cost $800K because it has fancy countertops and a gym with ellipticals that will be broken down within five years. It costs $800K because of local land prices and Boston's extremely low vacancy rate.

Ironically, you're helping out the developers you dislike when you perpetuate their advertising strategy of referring to high-priced apartments with basic amenities as "luxury units."

Solutions? The solution is actually pretty simple on a technical level but impossible politically.

1. Seize every golf course within 15 miles of the State House dome under eminent domain and build tens of thousands of cross-subsidized social housing units (similar to what you see in Vienna and Singapore) on the land.
2. Take zoning authority away from towns and give it back to the state. The state then does a Japan-style zoning reform where they define 10-15 different types of zoning categories, and local governments can have input on how those categories are applied locally. This makes permitting and construction cheaper and easier because you don't have every special snowflake town creating its own arcane zoning rules which means that all 351 cities and towns have to be approached differently with a legal team and political connections to get anything built.
3. Institute zoning minimums near public transit stations, and once that's established pull a Hong Kong MTR by using the "Rail + Property" business model to get real estate developers to fund public transit extensions along dense and valuable corridors.