That requires a bit more wealth to start with though, right? With 20-30% equity, the number of people who'd be able to afford a multi-family building (at least where I live) is tiny, and has a large overlap with those who can afford multiple multi-family buildings, I believe.

What's somewhat more common in Germany (at least in the rural areas) is having a single small apartment inside a single family home that was usually rented to workers.