Circle of Inevitability宿命之环

Book 1 ended with Klein becoming a god. There's not much path to climb further from here. You want to give reader the satisfaction of following an underdog protagonist that climbs higher and higher overcoming obstacles he couldn't before. The book about someone who sleeps all the time and can only influence world through answering prayers would be too boring.
Like sure, there's Above the sequence level and technically you can become the source, but there's no incentive to climb above level 0.
It would be like 100%ing the game compared to clearing it for the first time in book 1. It could have some good moments but it just wouldn't compare.
It's normal practice to use a reset after character climbs to the peak when you want to write new stuff in the universe. It can be MC losing powers or creating a clone to level up anew but with different rules or just following a different MC, like we did here.
High level puppet master boss you are talking about is much better as a secondary character rather than main one

1. Book not being ALL ABOUT ME is usually a sign of a comprehensive story. Because in real life, most of the time - whatever is happening is not about you and you are getting dragged into the story of someone else. Even in first book, the entire first act was the stage for Ins Zangwil and his book, show casing their abilities - and I would argue that his team and Aizek had much more agency over the story than Klein.

Sure, it gets better as he gets more powerful, but he was never the one to choose the plot of the book, from Amon to Evernight - everyone had their designs on the plot.
Now you also run into an issue of it being a second book. With Klein building an organisation and having me various people - naturally - all those people will be old monsters with high agency, because people already know them and want to see them again. And with time passing, it's natural for them to be even stronger than at the end of the first book - which means all of them are already high agency late game characters.

2. Book 1 ended with Klain becoming a god. If he's the focus, there's nothing to write about. From the first book, we didn't see gods proactively interact with the world. If it was 'sequel' as you describe it, with same characters and same focus, there would be nothing to write about. We reached the ceiling, we need to expand in breadth rather than height.

That was my biggest problem because volume one of this was absolutely perfect but the moment volume 2 started for a while it was a big drop then it started rising in quality higher and higher until by the late middle to end of volume 2 it became just as good as lotm

Spoiler: klien wakes up in the last stages of coi, it's worth a read, it's fresh, gives a insight of trier and intis and demonesses. And you already know what Roselle said, "taste of a demoness ain't bad"

Honestly the best thing you could do is read it it's still peak, and the volume 1 for coi is in my opinion better than lotm's and it only gets better. But if you still want to know