@resjudicata I don't necessarily disagree with your overall conclusion but there is a mistake in your working. The rental property is cash flow negative, but not necessarily an overall loss. Every month he makes a payment he has more equity in the home, which is a part of his net worth. And the longer into the loan term he is, the more the portion of equity he gets with each payment.
Whether it's still a loss or not depends on the actual numbers. It would take more than head math to be sure, but I would guess it unlikely to be a loss in the long run unless the interest rate is really high over prime, or he missed out details like high maintenance costs (or something devalues the house, but that's hard to predict). As a thumb suck estimate people tend to be net-worth neutral on a home loan for their residence after about 7-8 years, positive after. If it's a rental the point should happen sooner.
Homeloans are also an inflation hedge in the long run. Levy, maintenance, fees, etc, will tend to rise with inflation, however the bond payments will not scale up with inflation (inflation is a factor in determining the prime rate, but it's not a linear relationship. 5% inflation doesn't mean your bond goes up 5%. It's likely eventually his bond payments will decrease even when there's a positive annual inflation rate, just difficult to predict when it will happen), while rent tends to rise at at least the same rate as inflation (assuming no price shocks).
Everything else mentioned, especially about considering opportunity cost, are very important considerations. And an investment being cash flow negative can still be a problem even if overall net-worth is increasing, depending on the situation.
Personal opinion I'm very biased against directly owning property as an investment, unless you have some sort of edge.
/@paedwards