Yes, we're not talking about reality, we're talking about the measures of it. A metric would fall down on corner cases, so identifying the corner cases is how you determine if a metric is a good one.

"% people owning homes" is maximized by joint ownership, as well, but the corner cases are interesting: It is lower with big families living together or when anyone rents.

On the other hand, the "% homes lived in by owner" metric falls down in a much more realistic way: When there are fewer homes and they are lived in by owners, you can still have 90% of your people renting apartments while this metric hits 100%