Seattle has one of, if the not the biggest real estate bubble in the US
This means the median income to house ratio is roughly 1:5.5
This is fairly standard across the US, and was true even 20 years ago.
For example, in 2000 the median household income ($46k [2]) and house price (~$240k [3]) ratio was roughly 1:5.5. This ratio held true in 2024 as well with a median household income of $83k [2] and a median house price of ~430k [3].
As such, the cost of buying a house as a ratio of household income hasn't changed. The only thing that has changed is the perception.
[0] - https://data.census.gov/profile/Seattle_city,_Washington?g=1...
[1] - https://www.fox13seattle.com/news/seattle-top-cities-home-pr...
[2] - https://fred.stlouisfed.org/series/MEHOINUSA646N
[3] - https://www.fedprimerate.com/new_home_sales_price_history.ht...
Edit: This page has a historical slider that you can go back and see the price to income ratio of various metro areas over time. If you go back to the late 90s you will see overwhelming dark blue (dark blue is <3.0). https://www.jchs.harvard.edu/son-2025-price-to-income-map
Also note that the study you mentioned is comparing prices in 2018 with two recession recovery years (2011 and [edit: typo] 1988 - the year of the S&L crisis), which is an unfair comparison against 2018.
[0] - https://fred.stlouisfed.org/series/MEHOINUSWAA646N
[1] - https://www.huduser.gov/periodicals/ushmc/spring05/ushmc_05q...
If two partners are buying a house together (a fairly common occurrence) per capita ratios would treat both partners as an individual, but a household would help fix for that discrepancy.
Median household incomes take into account households of all sizes (1 person households to n-person households), and if you compare against median price, you can help reduce the risks of outliers tainting any comparison.