Having something really powerful that would solve your problem really easily doesn't necessarily mean that's what you're going to use to solve said problem. Because there's a myriad of other things that could do it without going too far. By far the most important thing is not the ability itself but the person with said ability, his or her decisions and moral fiber.

Powerful as the she may, Kotoha has never been able to brute force the problems that has arisen in the story she's from. Either it be a limitation of her understanding of her own ability, or a limitation of the ability itself... I have no idea. As quoted "I'm a powerspeaker, If I say It'll hit, then it WILL hit" yet in said scenario the shot she fired was going to miss if not for the fact the local God made the current weather's wind pattern favorable. So this does afirm that what she says does't always go.

While not my intention I believe I have just gone to the opposite end of the spectrum from Normal guy Guynemer who's going to be such a liability that he'd be relegated to filler material to Kotoha Isone who's apparently so powerful that it could make things trivial.

But please, don't be so caught up with the capabilities of a character that you overlook the interactive potential of said character. That's the primary reason I like roleplaying in the first place (and especially crossover roleplays).