Been hunting in Justice for a while now, and everything seems to have a loot item it CAN drop, they are all incredibly rare however. I have seen few duplicates, even though I usually spend a couple days per wing clearing mobs.
High level guards tend to assist in a larger radius. so if you are in Gaoler areas, or beyond them, you are best pulling the prisoners back to a sentry area. In sentry halls you are safe from most adds if you move back into the corner of a room. I do find that I get a lot of adds (rats and guards) when I have pet up, but generally none if I leave pet at home and solo.
What you say is true for the prisoners, but the caves follow different rules, B) Named mobs with rare/common drops. And there are no sentries or such just Geo's/Stonegrabbers/Larvae/Beetles
this drops off the named Geos/Stonegrabbers which generaly spawn in the alcoves in the caves.
Alla goes w/ what lvl could possibly solo the mob, many of these are wrong (sorry Allak, don't mean to bash on you at all, I understand it's most likely just databases feedin offa one another). And I am still assuming that allak hasn't raised lvl cap on site to 65, so all uber mobs will say 60 as lvl to attain. Look at mobs like the King in Chardok, he's a 60+ mob and check out his epic piece it will say 60 as lvl to attain. I've raided Chardok with my guild many times (and only 40 or 41 for all of em, yay), and we have always taken down at least 2 of the royals (cept for first raid, first time most of guild had been to Chardok not sure what to expect).