Mortgage payment vs. household income is probably the best way to assess affordability.
Except that effect and cause are counterintuitive.
People bid against each other on houses to the limit of affordability (maximum payments). With somewhat different dynamics for existing mortgages.
So house prices increase if income increases.
And house prices increase if interest rates fall.
And house prices increase if mortgage terms are made longer.
So affordability doesn't act like you think it might, because how people compete really matters.
Mortgage payment vs. household income is probably the best way to assess affordability.