You're not wrong, but honestly I can't really forsee how you're suppose to beat up the 5 final mobs with only a single character *because reasons* with the melee weapons, including that they each have ~1500 HP each, and most weapons only hit for around 50~60 per swing...vs a magic spell that rapid hits and has a big finisher worth 300 damage towards all targets inside of it, and lets you stay mobile to dodge everything. I think the balance for bosses in earnest is directly tied towards how good she is, and using the other two is a direct nerf towards your ability to handle such. Still, I need to beat this game many, MANY more times to see the full curse/blessings list...and I'm not too sure it's -worth- it, even if a few icons looks like they might indeed alter gameplay in creative ways...
There is some pretty fun ones, and you can even force yourself into a solo only run i imagine through the usage of the friendly fire curse, though haven't yet tried it myself. That said, Dorothy is definitely the largest power house of the group, save for some specific instances where Nellie with the proper buffs, ESPECIALLY with the Cursed Sword on high impurity just wrecks things, with I'd say the general weakest being Sera, albeit, she's also seemingly got the best move set for dealing with general mooks since she really doesn't spend much durability to kill things, and is speedy as all hell, something both her and Nellie share.
That said, Dorothy with any of the AoE spells thorns, thunderclaw in particular, or poison cloud can make pretty easy work of the final fight, though, it does require some intellegent running about or well timed dodges given her lack of mobility in raw speed. Nellie also, as I kinda was forced to discover on my first playthrough, can do pretty well with her AoE fire burst, especially with the added bonus from an altar that caused items to take less deterioration, and you absolutely WANT to keep her starting sword for the end game bosses if you can, as its durability is higher than anything I've found I'm pretty sure.
Interesting thing to note though, whether its intentional or not though I'm really not sure, but during the final phase of the ending boss, you can actually swap between all your downed characters, just you can only control one at any given time as long as they aren't 100% impured. So, if you're in the middle of a grab thats not gonna be seomthing you can get out of, or, are about to lose on one of your other characters, you can merely swap to another. This is how I managed to win, as with Nellie I took out one of the enemies, severely weakening the rest of the group before getting caught in a grab that would have been GG, before randomly trying to swap characters and was suddenly running around as Sera, then immediately swapped to Dorothy and the half bar of thunder claw I had from the Katana weapon managed to see me through pretty easily.
All in all, I'm pretty happy with the game honestly. Its short, sweet, and perfect for some time killing or just general good lewds whenever I'm on the mood, and the gameplay itself is pretty fun if a bit simple. Haven't really tried to master dodging yet as, especially on Sera and Nellie you can bait out attacks pretty easily and go in for a combo that will then stagger, with the best strategy being I imagine to use either of them and save most of Dorothy's super damaging spells for the final bosses throughout the end game.
My only question now is when will we see a tub only spell run?
Edit: Just for some clarity too, don't remember exact numbers but the cursed sword was swinging for somewhere around 260ish damage, and the AoE itself while I didn't get valid numbers, easily chunked the enemies pretty significantly, though given the wind up time its incredibly risky as a strategy compared to much of the aoe hit and run tactics of Dorothy. Sera I havent messed around with enough to see if any of her charged attacks are strong enough to do much, though she does at least probably have the better attack string between her and Nellie.