Where are you reading that the Full 9 is safer? What’s the justification given? If the certification is the same then Bell would have to have come out and said the Full 9 is safer? Otherwise that might just be perception because of the removable chin bar?
Both very good helmets IMO though, don’t think you’ll go wrong with either from a protection point of view. Super DH probably more versatile if you remove etc bar and use it as a ‘standard’ helmet too.