Sounds like the point made in California with several parishes there: if you join an auto club, and the auto club passes bylaws saying that all your property is held in trust for them, and you leave, that does not necessarily mean that the property should go to the auto club.
At least here in NoVa, as I understand things, the buildings and property are titled to the parishes, and the big ones pre-date the Dennis Canon.
So far the courts in California have gone with the parish versus a diocese.
Maybe the only place/time a diocese might win these battles would be a parish that was a mission bought and sponsored by the diocese, then maintained for a large part by the diocese.
Maybe we or the parishes in a diocese own that diocese after decades if not centuries of paying the diocese so it stay afloat financially.