Agreed. As much as I enjoy the read, it feels like it just spinning its wheels. And in any arc, even if "boss" is taken down, there is another boss, that is basically the same, that will pop up in the next arc.
Like in "child soldier" related events- they took down the old boss, but not before he sold the camp to another guy, and now another guy is fulfilling exactly the same role, with some sprinkles on top.
And after resolving each situation, nothing really changes. The status quo stays the same, people stay the same, and there are some moments that suggest progress, but a few chapters down the line everyone still acts the same as before.
Well, it's not a big investment, so I'll keep reading, but it's a bit disheartening.
The way I see it is that they don't have a lot to work with. You have a child soldier in modern day Korea. You have already 3 demographics of "enemies", political/bodyguard related, gangs, and those connected to his past. And this story was build on the sole premise of the MC being a one man army who is the best in the business of ass kicking.
You have some options as a writer here, but you also have some clear boundaries to work with too. You can't just have the MC open up a flower cutting shop and turn this into a SoL, no violence, peaceful story, as that's not what drew in the initial readers, and will quickly end the series, as that will just get boring for everyone who came for the action story (which would be most of us).
You also can't have the MC just repeatedly fight the same enemies over and over again, because that limits the uniqueness of the plot. Though that impact can be dampened when you make distinctive differences to the set-up and enemy organization each time (which is what they currently are doing). But that isn't a perfect solution.
A d you definitely can't just add new enemy groups, or else this turns into a "new villain of the week" kind of story, and no one wants to see that, because that drastically shallows up the story when you don't have a large cast of "good side" characters to counter balance with.
You also can't move MC to a new location, because it's the entire premise of him being "home" that sell this. If MC is constantly on the move, then it just becomes a manhunt. But if he stays in one location, it becomes open to defensive plot lines, counter offense plot lines, rescue plot lines, etc. It also opens the potential for a multitude of "uniquely tinted" scenarios to work with, especially because he is based in a normally "safer" environment of a modern day city, and not some unknown forest or desert somewhere in the world.
I will say that the story has lost most of that interesting nuance of no one knowing who MC is or is capable of, which I understand was going to happen eventually. We know MC very well now, and so do most of the main cast of characters.
What the author should maybe try doing is some more world building. Expanding the scope of things may give more opportunities to make a new scenario. It kind of reminds me of John Wick in a sense that the first movie was great, with most of the loose ends wrapped up. But then they made 2-4, which expanded the knowledge and rules of the organization, and added in factions and different groups, deepening the viewer's understanding of that world. Sure, some of the current characters have some pretty detailed history, but a lot of those details are superficial or just glossed over with a quick aside only for explaining why something is happening. There is still a lot that could be explained further.
For example, we still possibly don't know all that much about this organization MC was part of, or why the Numbers are specifically much more capable than the others on almost a superhuman level. Which could very well be an avenue for a future plot line to take.
Maybe the organization was doing some secret drug tests with creating super soldiers, and MC and the other Numberd are the successes? It could help explain why he seems to heal very quickly, and could give a few new "enemy" organizations to work with, such as the would-be buyers of those super soldiers.