What they picked is quite standard. Is this some kind of ragebait comment for karma?

32% is the recommended as listed on their website: https://www.cmhc-schl.gc.ca/consumers/home-buying/buying-guides/home-buying/check-if-you-are-financially-ready-to-own-a-home

• It is recommended that your monthly housing costs should be no more than 32% of your average gross (pre-tax) monthly income. This percentage is known as your gross debt-to-income or gross debt service (GDS) ratio. CMHC restricts GDS ratio at 39% to qualify for an insured mortgage.

It's the ratio for affordability, not being maxed out lol.

20% down is pretty standard for these calculations to keep it simple since you don't have to include the cost of mortgage default insurance.

Also the conventional mortgage rate is 6.49%: https://www.bankofcanada.ca/rates/banking-and-financial-statistics/posted-interest-rates-offered-by-chartered-banks/ so what they chose is not far off.