@errorbit you know what? for your good faith, i'll answer seriously.
Essentially the problem is this: so far the main characters have struggled with very little, and what little struggle there was, was for comedic effect, now, in a comedy that makes sense, hence why i was enjoying myself, this wasn't konosuba where the struggle is the comedy itself, but see, ever since this arc started, the rules were flipped, now nothing can be funny because its all super serious, and what little comedy there is, is hampered by the fact that the consequences of it are so severe that the peril they cause cant be laughed it.
Now, if its no longer funny, what is left? a drama? a terrible one in that case, both of the main characters have done nothing but the stupidest, most illogical and out of character things possible, if it was one of them doing it or if there was a motivation for both to be that way (dark hair dude has close to no motivation to justify his current actions) it would be fine, but that isnt the case, so the drama ends up being incredibly frustrating due to how forced it all is, the story breaks its own rules, its own characters, for the sake of making us feel something.
but you know what i feel? anger, because its genuinely frustrating to have been made to care about light hearted characters through comedy only to be wrangled into a drama that comes out of nowhere and requires you ignore everything you liked about the story in the first place to buy into it.
One final thing, Konosuba has done serious drama in the past (i've red all but one volume of the light novel) except when konosuba does it, it makes sure to have comedy layered on top so that when someone does something uncharacteristic, it comes off as character development and not like the character suddenly changed completely, i can go into specific examples if you want but that would require LN spoilers and i'd rather avoid spoiling some of the best parts of that series, which the anime and manga havent even adapted yet.
EDIT: i realized that i forgot how to respond the question specifically, the reason why its a power fantasy is that so far the characters havent had ANY big problems and this is the first one they come across and its obvious the solution will be the power of love, a cliche that you can only invoke without being cringy if they characters are believably in love and not just "friends that find one another hot for comedic purposes"