لَا تَبِيعُوا الدِّرْهَمَ بِالدِّرْهَمَيْنِ وَلَا الصَّاعَ بِالصَّاعَيْنِ
Do not exchange one dirham for two, nor one measure for two measures.
The prohibition clearly condemns the prohibited usurious exchange. But the claim that no defective contract can ever have any proprietary consequence is a separate inference requiring its own argument. Prohibition, defect, possession, and transfer of ownership are different legal questions.
The Hanafi distinction between a void and a defective sale is important precisely because the unlawfulness of a transaction does not by itself settle every possible legal effect.