I feel that the total payment (P+I) indicates the true "cost" of living in a
house. That's why I'm saying that a jump in the rate from 5% to 6% "only"
increases the cost of ownership by a little less than 12%.

Fair enough. Most people are "payment buyers" when it comes to a home.

But, don't forget you're talking a 12% increase in what is, for most people, a
relatively major chunk of the household budget. The example you used in a
previous post examined a $100,000 mortgage and the payment went up over $60 a
month. Most people are going to have a mortgage 2, 3, or more times that amount
these days. Not all potential buyers are in a position to absorb 60, 120, or
180 additional dollars a month and will want some help via a larger discount in
the selling price.