If I’m being brutally honest – this book is a filler story. But it’s a filler story between some fairly important action in the last book (in which one mentor of the main characters betrays the school they attend, and therefore causes the death/probable death of two other mentors), and the last book in the series. So as long as the last book in the series lives up to the set up, I’ll be ok with it.
Our main characters actually absent themselves from the main action for most of this book, in a way that should gain them more agency in the fight to come, and definitely makes for an interesting meander off world. I’m very much still not sure how I feel about Alustin’s betrayal, but I do expect that to work itself out in the next book.