While I don't exactly disagree with your overall point, fire I vs light I is arguably one of the better balanced parts of new game+, with the former being cheaper to cast, having more base power, being useful out of combat, and being gated behind Charlotte not being in jail(+1 day, 400 gold,  lewds, or a 14 day wait) whereas deliver medicine is basically a freebie and light I is mostly useful for advantage.

Fire I also gates workshop level 5 if you have access to the refugee camp, which can translate to an extra ally level when clearing the Northern mine vault and festival of greed. This mostly impacts lower difficulties and early parts of the game where allies are quick to level.

More egregious are horror I and radiance I. The first only costs 10 points in new game+, is practically unobtainable during pure runs, and gives you a low-mana way to trip up enemy casters for defensive builds. The second costs 35 points, is pretty much unusable in chapter 1 due to its mana cost, and mainly serves to save(an admittedly large sum of) money unless you very specifically intend to chug another energy potion or two on Belphegor.

Another thing is the stat crystals having the same cost for all three stages. Changing something like a 5/5/5 cost of ATK/MATK to a 4/5/6 for +1/+2/+3 would increase the temptation for higher-score players to downgrade starting bonus stats for the sake of a skill pick, make the weaker tiers more accessible for low-score players who need that boost the most, and brings it more in line with the chapter 1 experience of escalating workshop prices.

Given that I've spoken on nightmare mode's poor balance in the past, you'd be forgiven for thinking I'm referring to it. I'm not.

Belphegor (Pure) is a nigh impossible fight on NORMAL/HARD without one of three things. New game +, drugs (especially bloodshot since lascivious won't offer much to pure) or star knightess. NG+ obviously shouldn't be necessary, but radiance is very strong. Star Knightess obviously shouldn't be necessary, as it's an instant-win crutch against anything and frankly defeats the point of playing. And while I think drugs are the most legitimately arguable since they do not affect ng+ points, and thus can technically be used on pure runs, I do not find this satisfactory. That a 'pure' run would require drug abuse goes against the very point of playing pure.

There is but one answer left. From day 1, Aura must desperately focus all of her stat-increases in to as much magic defense as she possibly can. She must save and bless every single vitality potion she can, specifically for this fight. Then, and only then, does she have a *chance* at standing up to Belphegor. The dual assault of Belphegor and Luciela deal indefensible amounts of damage to anyone not using the above 3 options. Only a pink run with ludicrous amounts of magic defense (thanks to lascivious' *past* use during scenes) can hope to defeat them without any of the above. 

There are many posts over months if not dating back to Belphegor's introduction to the game that discuss it's poor balance. People talking about how they have 60-70+ magic defense and still cannot win....because they deal like 50-60 damage each per turn against a character lucky to have 300 health. Meanwhile, especially thanks to Luciela's reflection spell, that amount of damage output will kill you even BEFORE you can take Luciela out, never mind taking on Belphegor's what, 8k HP? Can't remember what it has right now, been a while.

> the bar for nightmare might be something along the lines of "Auradev is able to clear this, so it's theoretically winnable."

Even that has proven untrue upon the introduction of Firestorm's final floor and boss.

> " Nightmare mode will kill you though :'D"

> It should also be noted that the deluxe edition has a built-in cheat console. This might be skewing the perception of some patreon players.

Frankly think it's skewing the position of the dev. Only god knows where they supposedly get 20k for tuition on a pure run.