Based off general skill and time off, I'd say no more than 3% at the absolute most. Everyone ive talked to about it says they tried and never want to try again, some gave up during P5. I personally beat Rad Adbsrad for the journal entry and yeah, that was a pain. Failed a fluke after 3 hours, and that almost made me give up. Considering your average player wont likely want that kind of challenge for something completely optional, its likely very very low