Earlier quoted context omitted.
Alternative investment is of course a thing. However, you're missing the point. People MUST live somewhere. Their only alternative investment is with regard to their down payment for money saved, or the amount of money that is (mortgage - equivalent rent), which is usually negative! The BULK (or entirety) of the money they spend on their mortgage is not money that would otherwise be available for alternative investme…
In my experience in the recent market (in a HCOL city in the U.S.), rentals (even only compared to the costs in homeownership, i.e. ignoring principal payments) are much cheaper than mortgages for an equivalently sized house/unit. That's the assertion of the article, and it rings true. You're right that the bulk of the mortgage payments, especially towards the beginning, do not go towards building any capital, which…
All the cost calculations should be based off interest only. The principle repayment is a cashflow issue - and a signifcant one at that.