I think each card should be playable by only one account per season. Anything else is really an exploit. Even though we're used to this system, it's essentially card inflation which brings value down.
IMO rentals should be something like this:
Owner sets total seasonal rental price
Price decreases based on the remaining days in the season
End of season all rentals go back up for rent
Very intuitive, logical, and practically impossible to exploit.
That makes sense. Functionally the same without mandating a full 14/15 day rental. Not a bad idea, but also not sure how much work it would be for the team to make a change like that.