I can say without a doubt that there is high wealth disparity in NZ (I have lived there at several points in my life). Public sector pays poorly relative to cost of living, and many private sector jobs pay below their equivalent overseas. It is absolutely necessary to be a dual income family, and many women are forced to have new partners they barely know move in with them, just to pay the bills. It puts women and children in extremely vulnerable positions. Also due to its small population and tight supply chain, wholesalers rake in massive profit margins. Once you include retail profit margins, you see prices up to 200% above other countries. Energy is also incredibly expensive, and you have to get used to being cold in the winter, or paying through the nose for electricity, as most houses have very poor (if any) insulation and winter temps do dip below 0C. One thing I noticed as a Canadian expat living there is how 'user pay' a society it is. There are very few truly 'free' events there, and most public fairs or gathers or festivals will have entry fees on top of paying for all activities. Its a beautiful place which can afford a variety of lifestyles and varied landscape, but it definitely comes at a high cost.

If I don't pay my mortgage, my home gets foreclosed. If a tenant doesn't pay rent, they're evicted. How can someone "not afford" their living expenses, yet simultaneously live there? As is the case with millions of people in Singapore?

Your point about real estate is spot on. As prices rise, fewer can afford it, so they leave. So according to this logic, if 5 million+ people live in an area...

Singapore's population is just now starting to decrease, so yes, so some people, it appears its becoming unaffordable.

If I don't pay my mortgage, my home gets foreclosed. If you don't pay the rent, you get evicted. By definition, how are people living a place they cannot afford?

Is the cost of living so high it probably sucks ass to live there? Certainly. You can find plenty of people living in closets in NYC for ridiculous prices. Looks like a shitty living situation to me, but they appear to afford it.

But how would that be more important than housing prices as a multiple of income? Whether other countries went up more or less, if housing was a lower multiple of income in Singapore, would relative increases or decreases be more important to you? I've added a source in my parent comment as well.

Per the study above, Singapore housing costs were 4.5 times income, whereas another city had housing that was >40 times income.

If housing started out costing 1% of your income, then increased to 6.5% of your income, that would show as 6.5 in the OP chart. Whereas if another theoretical city had housing costs go from 45% of your income to 60% of your income, that would show up as only a 0.33 increase on the OP chart, or ~1/20 as much of an increase, even though the final cost was ~10x higher in the second location, and even though the absolute change was 3x as much. But you can't tell any of those things when you're only shown relative increases of 6.5x and 0.33x.

The problem with the Greater Toronto Area is that there is tons of technically redevelopable land that aren't intensified because public policy shields single family homes from development pressure - this limits new housing to either the urban boundary, formerly industrial brownfields OR high-rise condos at very selected locations - which coupled with the rapidly increasing population is the cause of the problem.

There are some commonalities with Singapore though - in that housing is considered an asset for future retirement needs, which makes policy gearing towards popping the asset bubble unpopular to the subset of demographic/voters currently in power. But unlike Singapore where government public rental housing is a thing, it really isn't here in the GTA (or North America in general) for all except the lowest-income population. Relegating housing entirely to pretty much the private sector alone is a giant public policy failure.

As Ive explained, sprawling helps because it keeps both construction cost and land value low, while density makes construction cost and land value high.

Toronto doesnt sprawl nearly enough for Canada's insane population growth. They locked it inside the green belt. Which I understand why they would do that, but you can't do that AND add millions of new people, not without housing being a nightmare.