You make some good points but you are also assuming that someone that comes into money and has the choice to either pay off their primary or do something else will be wise with those funds/cash.
I’ve seen plenty of people that come into money and aren’t wise with what they do with it. Plenty of people blow extra cash on either bad investments or just spend the money foolishly. So you have to look at it from that angle as well.
Absolutely leverage can and does work out for people but it does people in as well. From my experiences over the past many years investing, I’ve learned that people are quick to tell you about all the great genius stock picks or other investments they have made that made great returns. However, they neglect to tell you about all the bad investments or stocks they have made that have lost a lot of money. (Especially on these message boards).