Can you tell me generally big examples of places where this has happened and things have gotten better?

That’s a really specific request, but sure: Vancouver empty home tax California Tenant Rent Cap.

Are you sure this is flat-area and doesn’t need to get multiplied by number of flats per building?

As far as I can tell this number is accurate, again if you can find a better (or more clear) source than what’s given on wikipedia I welcome it since this is a composite number pulled from housing reports in a primary language which I am illiterate in (and can only barely speak).