perennialism is based on three things: 1. selective reading 2. historical revisionism 3. blatant lies all of these may be found in the most recent perennialist gospel by saint h. nasr, which, keeping true to the above three principles, has been named The Study Qur'an. Logic and consistency are to perennialist discourse as fire to ice - it melts at the sight of them. The mad hatter might not be more logical than nasr or hanson, but at least, he is consistent in his illogic, not to mention utterly frank.
The Proof is complex and comes back to proving 1)The existence of a Necessary Existent Being who is Allah (swt) 2)Prophet Mohammad (صلى الله عليه وسلم) is a messenger of Allah (swt) 3)Quran is a book of Allah(swt) revealed to His final messenger. 4) It is impossible that Allah (swt) should lie. Our rejection of perrenialism is Quranic rejection and Quran must be shown as a true source of information and demonstrating this depends on all these premises.