At first impressions, this ending felt disappointing. The big bad enemy is pretty bland, the method of fighting it is boring, the majority of the characters are barely involved, and The System suddenly starts making the big decisions instead of the actual characters.
But the more I think about it, the more I can understand at least a few of these things. The Predator is supposed to be an incomprehensible existential threat, which is a huge challenge to represent. It can't just be, like, some guy: Galactus is huge, but not incomprehensible. The way it's been treated throughout the story is analogous to something like our real climate crisis, which is of a scale that most people cannot truly comprehend, and is so large that many feel that they can't possibly do something as an individual.
Which gets into why we only have our two characters here, Mo-ah and Seo Ji Han—and really, this whole ending is mostly about Mo-ah, since Seo Ji Han is primarily here just to tie in the conclusion to their romance. Mo-ah has miraculously been given the potential to actually deal with the threat, and the latter part of the story has consistently been about her coming to terms with the responsibility that comes with this great power. She's the only one capable of saving the world and everyone she loves and cares about, so it's up to her alone to step up. This is the climax of that journey about taking personal responsibility for what only you can do, which is a very sobering one. It's not really something to get hyped up about.
It's an ending that won't be to many people's tastes—it's not even to my own tastes—but I can respect it. Hopefully the side stories can liven things up with some wholesome vibes with everyone.