About a dozen years go the factor was roughly 2:1 - CofA fixed wing was achieving a fatal accident rate around 1 per 60,000 hrs compared to 1 per 25,000hrs for permit aeroplanes. Microlights sat between at around 1 per 50,000hrs as did gliders and light helicopters.
Since then however, all classes have improved a lot.
CAP 780 shows the most recent stats published by the CAA, but it doesn't separate out CofA and PtF light aeroplanes. Scanning chapter 5 however, there are clearly far more CofA aeroplane accidents than PtF aeroplanes. Okay, there are a lot more CofA aeroplane, so this does indicate rough parity between the two.
A significant risk of in-flight breakups is the only real reason why you could justify requiring PtF aeroplanes to observe a more restrictive standard than the "vanilla" rule 5. That risk is tiny but basically equal - CAP780 shows two to PtF aeroplanes (a CubyII and a Europa) and two to CofA aeroplanes (a PA28 and a Rockwell Commander). The microlight fleet had one in-flight breakup in that decade, to a type which was subsequently (and remains) banned. Small numbers, all statistically insignificant. So, rule 5, unammended, now applies to all fixed wing aeroplanes - light and microlight.
G