Won't comment on the merit of his argument but there are a couple of factually wrong things here:
Prince didn't exploit any legal "loophole" to get his masters. Masters revert to the artist after something like 35 years from date of copyright and a few of Prince's albums had already aged over to him. Realizing that the bulk of his seminal work from the 80s would soon transfer over, Warner Brothers saw an opportunity to monetize this event and simply accelerate the transfer of the masters in a single transaction rather than lose access to Prince's catalog by piecemeal.