If it was 1965 this might be good advice. In 2021 it is disengenuous (at best) on multiple levels.

The bottom line is you should invest at the highest known interest rate for the long term. The key points here is that you know your rate for the mortgage (if it is fixed) but not the future value of your home.

Assuming the housing market will grow steadily for the next 40 fucking years in 2021 is ridiculous. We had the dot com, Wall Street and Covid crashes all in the last 20 years.

Assuming your work life will remain steady for the next 40 fucking years in 2021 is insanity. Again, if it was 1965 this might be a decent assumption.

Also super disengenuous is not noting that compound interest works both ways. Changing from a 20 year (what I always recommend since I'm not a loan officer) to a 40 year loan means the interest on your loan will be compounding for 40 years instead of 20.

If "Russell" is 25 or older, he will not pay off his primary residence until after he reaches retirement age. This basically locks Russell into a situation where even if he and his wife do well for 20 years and think they'd like to change jobs or just work less, that mortgage will still be hanging over their necks for another 20 years!