I don't think the overworld is more difficult. Difficulty wise it feels the same as when I was leveling 1-50 with ninja and bard and didn't have a bunch of dungeon gear tucked away. I.E. it feels about the same as the normal game before we out ileveled as far as 'this is how much I can pull before it murders me viciously'.

HP amounts do feel a bit ridiculous, though. I feel like things should still be dying pretty quick with a zeta at 52-53, but they aren't and I truly feel for anyone who has to go collect bear asses by killing mobs with a 115 weapon. Those are never fun/engaging/interesting quests and making them take longer by padding out overworld HP amounts doesn't create challenge. It just makes things vaguely more annoying.