You can find a thorough study of PP together with other popular portfolios at Permanent Portfolio. According to the author of this website, the SWR(safe withdraw rate) is as high as 5.3% for 30-yrs retirement.Right. These are the parameters of the problem as it has been studied so far.
This isn't to say that other methods cannot work. Maybe different rebalancing strategies, or living off dividends, are completely viable alternate solutions. However, these studied did not consider them.
Similarly, the kind of things I do (permanent portfolio / risk parity) have not been thorough studied either for withdrawal and capital depletion. I can't say conclusively that it's a good idea, or that it's any better than classic asset allocation for living off capital.
And if I was a professional, I would absolutely not be able to advise anyone to use these methods on just a hunch and my amateur analysis.