As it stands, it's a huge save-scum mode, especially as a result of how utterly weak allies are in it. For the most part they're naught but meat-shields, there just to guard while Aura deals several times more damage. Charlotte offers some decent utility with heat up, but dies if an ant breathes on her, and Paul's pierce is about the only reason he consistently contributes. John is especially bad on hard mode, often barely contributing anything outside of a single protect for Charlotte to get a second heat up. The other utility he should provide, early AoE damage with slash, is left down to chance because enemy agility on hard mode is incredibly high. Given that boosted bosses on hard are pretty much guaranteed to one shot anyone not named Aura, the ability for allies to do anything but block after turn 1 or 2 of an advantage attack (depending on boss pattern) pretty much doesn't exist.
In my opinion, hard mode overall has a much better flow than normal mode, (which I argue is too easy) especially because of the rate at which willpower decreases. You alternate between curse and no curse at a much more rapid rate, which creates a better flow between spending cursed days clearing out weaker enemies you've avoided and learning multi-day abilities, and then acting out a pink scene before utilizing what you learned during your cursed period while you're strong. Even optimizing days where you use day-long items or flash bombs for particularly strong bosses does feel much better.
Ultimately there are a few suggestions I have that I've thought about and settled on as good balance changes for hard mode. They should retain most of the challenge, but also make the game much more consistent on the side of allies.
1. Remove the 30% enemy bonus from agility and luck. While it's good that enemies are stronger, the speed and luck they have damage strategies that still work in hard mode, but are left to lower chance than what is reasonable for most allies. Even enemies with only moderate speed (sometimes even only 2/3rds of a characters speed) will, thanks to their luck I assume, out prioritize player characters on a more regular basis than you would expect. Also thanks to high luck, on a more regular basis than what you'd expect also, enemies that are blinded repeatedly make successful attacks on characters with tactical advantage. Two effective dodge modifiers and probably upwards of still hitting 75% of the time.
2. Defense and/or Health increases to allies. Aura has the ability to deal with much of what hard mode throws at her through proper workshops, tactical advantages, drugs and potions etc., but allies often struggle to survive even a single hit they're blocking, especially magic or critical hits. Their damage output/roles in fights doesn't require consideration in my opinion, but with enemies buffed 30%, especially in John's case, survivability is inconsistent. I would suggest even a compromise where only John's defense/health receives a 10-20% starting stat buff. There's genuinely an argument to make in favour of a slime over John with some decent investment.
3. Improved guarding. There are a lot of things in the game where the agreed on counter-play is considered to be blocking powerful attacks, however due to the weakness of allies and sheer overwhelming numbers buffs give enemies that are already 30% stronger, blocking is far from enough in many situations. Blocking in hard mode should be stronger to better reward proper defensive response. Quentin exists early as an example of this, but it quickly becomes obsolete in hard thanks to the absolute canyon between weak ally characters and powerful enemies.
4. I would even consider removing the increased reading requirements or workshop prices, or increase money drops from enemies as a 'reward' for hard mode. While the increased challenge of the game is fun, enemies are strong enough through their stat increases without weakening you more through less workshop opportunities/ability to actually use your materials, and feeling disincentivized from reading for a week just to receive 1 stat point. Why would I read a book for a stat point when I can work in the workshop that same duration, receive over 20 bonus health, and have money left over after a workshop? (Speaking of, working there is a great use of cursed time, so it's rather deceptive Aura says it's not!)
Anyway, I hope someone of some note sees, reads and considers any of these suggestions. Genuinely like the game a lot, and I've spent most of my time in hard mode trying to figure out what works and what doesn't. In my opinion, the above changes really help refine the pain points of hard mode that turns it from a fun and challenging strategy RPG, in to something that borderline if not outright necessitates save scumming to handle your weak allies.