@CrusaderJerome I don't disagree with what you said, but I think an important caveat is that there's not anything that anyone
from this world can do to stop her. Let's not forget that the most powerful fire user alive is just a flamethrower spell user who figured out that a jet of air makes the flame burn hotter. The third princess is almost certainly just some chump that's figured out something basic that is unknown to this world, like magnetism or something, that she's adding to her earth magic to make it seem vastly superior to everyone else.
The only reason the MC struggled with eyepatch girl's dark magic is because the nature of grudges born from the human soul wasn't a subject the mages from his world were wholly familiar with, since the fundamental nature of humanity was still a mystery, and thus the fundamental nature of curses born from the human spirit also remain unknowable. Even then, he still knew a hell of a lot more about it than she did, and one would assume far more than anyone from this world would know. They're so confused they think darkness is an element, when it absolutely is not.
Honestly, the only thing I don't like about this manga is that the demon race seems to be powerful enough that they should have just rolled humanity over by now. Anything that could give what amounts to a Nasuverse mage a serious run for their money in a fight should be able to effectively conquer the entire planet of level 3 D&D wizards this setting seems to be comprised of. I assume there's more to it than what we've been shown, and some of the spoilers some novel readers have thrown around do suggest that there is in fact more to it than that.