That article you linked is just straight up wrong, it says Tokyo grew by over a million people in the last 10 years. 2013 population was 37.116m and 2023 is 37.194m, that's a growth of only 78,000 people over a decade, and equates to a growth rate of 0.2% over 10 years, or 0.02% per year. It peaked in 2018 and has been declining since. https://www.macrotrends.net/cities/21671/tokyo/population
Yet prices still went up around 20% over the last 5 years. https://fred.stlouisfed.org/series/QJPN628BIS
They say it's affordable, but they also forget that affordable doesn't mean "cheaper" it means "cheaper as a percentage of income" The average income in New York is almost twice that of Tokyo. https://versus.com/en/new-york-vs-tokyo/avg-salary
I'm hardly new to this topic, I've lived in Japan multiple times. Every time I see an article about affordability in Tokyo it's written by someone who has never actually lived in 120 square feet. I've slept on a 1 inch thick mattress that I had to put away to use my apartment during the day, have you?
Urban planners are not who we should be looking to. They're given direction by politicians, they don't get to set the policies that would optimize for affordable housing.
Affordable housing doesn't exist for one simple reason, there are too many owners who benefit from using their housing as an investment. 65% of all residential properties are owned by the family living in them. Until we remove the ability to make money off simply living in a house, they will never be affordable. Convincing voters of that is going to take another few decades at the very least.