I think they're not considering how the portion of rent that only goes toward the mortgage is still profit despite it not being accessible until the home is sold or a loan taken against its equity.

It's absolutely relevant if you know how a mortgage works. Payments are ~75% interest in the first decade. I'm not going to have enough equity at that time to make a profit after all the money I put into the house. I'm looking at a $50k loss if the market stays steady. Still cheaper than renting, though.

Yes, my tenant subsidizes my living costs. That's the point of a duplex. I set the rent at what I thought was fair, given my expected losses and the work I put in.

There's no shortage of housing here. If my tenant wanted to, he could buy a house right now. He's waiting until he retires, specifically because he doesn't want the responsibilities of home ownership while he's still working.