Dungeon 3 wasn't that big of a deal; it's still quite easy to sneak through most of it. It probably wasn't a good idea, but I couldn't help but equip and try everything I had a free slot for... but that didn't cause too much of a problem. I had an early casualty on the first floor, and restarted. Then Sayaka fell early on the second floor, but with no way back, I pressed on... and proceeded to open all the chests and beat the boss. It probably helped that I was able to clearly identify which enemies were trying to add extra curses, and focused my attention on them whenever they showed up.
The Collar item was probably meant to make sneaking harder, I guess? In Hard Mode, its movement speed reduction is actually pretty excessive. Both surviving party members were collared after the final battle, and it would've been really obnoxious if that'd happened earlier without a good way to mitigate that speed debuff. As per my original run, the title grind remained pretty straightforward with the ability to transfer de-cursed items (the "Curse Remover" also helped!), and it was the XP grind that took longer, thanks to the lingering effects of anti-XP curses.
Dungeon 4 was unpleasant the first time, but you'd made it a little easier for Casual mode since its initial release, as I noted earlier. Not so for Hard Mode! By far the most brutal change felt like locking all the grates; without being able to open up faster routes, my first shot at the boss was Kyouko solo, with just her arms free; everyone else had been mummified and defeated. There was a switch in the boss room just before the boss, but it seemed to do nothing? I also saw the "hilarious joke", and saved just to confirm that it did exactly what I thought it did. Her buff/debuff attack cycle wasn't bad in many of the earlier fights, but was laughably insufficient for the boss.
The level cap here was particularly noticeable, just two levels above where I was exiting Dungeon 3. There were LOTS of pills here, and as predicted I didn't need any of them; I was stuck here long past hitting cap. Hopefully, they'll be useful later.
Once titles started rolling in, I applied gear; Mami got the Greater Tiara, Sayaka got the Lesser Tiara, and Madoka got the obviously-cursed "Queen's Tiara" (being the least-useful mummy, she could at least be an okayish tank with the Slave Collar). Fighting the boss with effectively one and a half characters was hard, but Mami's debuffs and Sayaka's physical damage proved just barely sufficient; Mami beat the boss with 6 HP left (the exact amount of damage the boss had been doing to her with each hit). With no paths backwards opened by defeating the boss, it's a good thing that everyone had gotten their titles by that point; I would've hated to have to do all that again!