@Evron
While I absolutely don't think anything remotely close to that would happen in this kind of story, your revised version is at least more in line with Momo's character.
Just a few points that need to be considered:
-It happened 7 years ago. So Momo was only like 8 years old.
-Momo acted in a group.
-Using a wish to save the world would imply the system can automatically solve all issues, which would make all magical girls superfluous.
-If they used a wish, then nobody would even be aware they did it in the first place, right?
-The amount of points needed to make a wish of that scale would be extreme. Momo would never find enough demons worth any points that are also willing to sacrifice themselves and as we just established, she wouldn't hunt innocents.
I dont think using collection points to solve problems is viable in the slightest, considering how little demons are worth, especially as the points needed scale exponentially with the wish. It doesn't sound like something that is used very often at all. I've seen people say Sakura may have gotten rich through a wish, which allowed her to buy most of this town's property, but that's the closest to an actual believable use I've seen. Mikan clearly never made enough points to wish for her curse to be lifted for example, despite obviously having experience with sealing dangerous demons from what she and Momo talked about. I assume threats on the scale of snake goddess Mizuchi would be worth a lot, but as Momo said, most modern Dark Clan are on Shamiko's level.
------
My guess is that the threat to the world was either not coming from a Dark Clan member, but rather something more abstract in nature (Hence why Momo doesn't exactly think that saving the world is an accurate description). Or it was (a) magical girl(s)/navigator going rogue. Momo's injuries led to deep scars and according to what she told Lilith the only things that leaves such deep marks are ether based attacks, because they damage ether bodies. Of course some demons may have ether based weapons too... after all Dark Clan are not a homogenous race or anything. If both of those are inaccurate I can only imagine it was an accident...