Question

Good evening!
There is a dispute among the medieval authorities (Rishonim) whether a rabbinic acquisition is effective on the Torah level, and my question is: according to the view that the concept of “ownership” was a metaphysical, ontological legal status, then it would make sense that through a rabbinic acquisition this does not occur. But insofar as “ownership” today is only a legal relationship (and especially according to Rabbi Shimon Shkop, for whom the laws of ownership are a category that precedes the laws of the Torah), it is hard for me to understand why it should matter by what mechanism we established this relationship—at the end of the day he is the owner, no?
And to describe the absurdity of this, I’ll give an example: in a case where the seller regretted the sale after the acquisition, is it conceivable that the buyer would violate Torah-level theft? (Of course, were it not for court-ordered confiscation, and were it not for Rabbi Shimon Shkop’s ruling regarding theft.)
Thank you very much!