Agreed. I'd go further. This obsession with ownership has always struck me as a peculiarly American thing, perhaps related to the absolutely central role of private property in the USA's history. In other cultures the concept of private property is often diluted somewhat by social obligations and counter-obligations. But that aside, the term is already very imperfect for the reasons you describe.
Perhaps the better word is just "control".
Isn't it the same thing?
Stuff you fully control is stuff you own fully.
Stuff you don't fully control is stuff you don't own fully.
Stuff you fully own is stuff you fully control.
Stuff you don't fully own is stuff you don't fully control.