> after 30y you end up with a house that worth $1M

In his video, Sal Khan did an apples-to-apples comparison: He compared the net out-of-pocket costs of (i) an interest-only mortgage in which you build no equity, and (ii) renting, where you likewise get no equity.

If you also want to build equity in your house, in addition to merely paying the interest, then that's an additional out-of-pocket cost (which unlike the interest payment is not tax deductible).

That's not to say his numbers are realistic approximations. But his basic approach to comparison seems sound.