I like the definition you mentioned as well. The problem is that it's very hard to get good data on it. The first link certainly doesn't do a good job of anything, I immediately see it has the common problem of looking at prices rather than monthly payments. That's just bad academics. In the Netherlands for example I get 1% interest rates. In Denmark interest rates are negative. In the US they're 2.8%. In NZ they're >4%. That leads to wildly different affordability at the same price-to-income ratio. The graphs of the affordability ratings (based on only price-to-income) declining are a complete joke as it completely ignores the interest rates dropping hard, leading to higher borrowing capacity and lower payments per dollar borrowed.

The other links I haven't all studied, but for example in the Netherlands where I'm from Amsterdam, the situation (and the article) is entirely not in line with your definition.

For one, jobs aren't all centralised around Amsterdam. The Netherlands has a concept of the Randstad which includes all the four major cities in the country, which all happen to be within a 60 minute commute from oneanother. All the little towns and villages within and surrounding this area comprise of about 60% of the country's population, again, all within a 60min commute. It's thereby silly to look at the housing market of just Amsterdam, when the majority of the country lives in a close commute from jobs centres and doesn't need to live in Amsterdam. Note that from the centre of the country, the closest border (of the country) is 57km away and the furthest border is 175km away, that's how small this place is. It's misleading to look at prices of a single capital city and ignore the fact most of the country lives around the corner with prices that are <50% of that place.

But supposing we look at Amsterdam, the article then makes a crucial mistake by comparing a single Dutch person to an average Amsterdam house. Since when is a single Dutch person an average Amsterdam household? The average household in the Netherlands has 2.2 people, so you may double the borrowing capacity. And second, Amsterdam's owner-occupied homeowners aren't making average money because they've got Capital city above-average jobs. If you live in Amsterdam as a home-owner, you're exposed to jobs that pay far more than the average joe jobs outside the capital. The average income is about 55% higher (see CBS figures).

In short you're looking at double incomes which average 55% higher in the average Amsterdam owner occupied household, or 3x the income. Given how the borrowing capacity works here that translates to about 3.5x more purchasing capacity than the article mentions.

The article also fails to differentiate between average income in the Netherlands (which includes people on welfare, people without jobs, students, people who work 20 hours a week etc) to average full-time salaries, which are typically the group looking to buy a home.

One thing people often fail to acknowledge is that when a claim is made that X is unaffordable, that the fact prices are so high actually may signal the opposite. The fact home prices have increased by hundreds of thousands despite borrowing rules not having changed much, means there's actually a lot of demand at these prices. If nobody could afford these expensive homes, prices would've come crashing down. There's been a record amount of homes sold in the Netherlands last year, the majority of the country is home-owner, and LTI and LTV rates have been trending down the past years (indicating people are actually using less and less of their borrowing capacity).