Got curious and tried it myself. Went from 67 to 68 in about 20 minutes doing 4 Hardcore Magatsu runs repeatedly to train up my Bouncer levels, using all my best exp boosters which as you say, do not diminish at all. This may be slow, but looking at it from a pure soloist perspective of exp gain rate vs time, its a fast option once good at it. This makes me very happy as a way to level both classes and rings if I'm in a solo play mood.
Thanks for sharing this!
Story PD(profound darkness) gives similar results for those who don't like dealing with magatsu. It can be harder and slower, or easier and faster depending on class used and how familiar you are with the fight though.
Edit: Here's a screenshot done on pso2day with +600% exp total and level 65 scaling
Ok. so I haven't done hardcore PD because I was stopped by level 80 hardcore gemini. How do you get it to scale to your level?
That's weird, because the only story quests currently in NA that scale to 80 on hardcore regardless of your level are the last 2 EP3 CH4 quests.
EP3 CH3, Story PD (and the double/gemini before that) scales to minimum of 60 if you're below 60, and scales to whatever level you are if you are above 60.
EP3 CH1, Story Magatsu scales to minimum 40 if you're below 40, and whatever level you are if you're above 40.
Edit: I don't remember EP3 CH2 double/gemini fight's minimum scaling on hardcore, but I do know they still scale to your level if you're above the minimum. (I personally double checked before posting this.)