The Rain Wild Chronicles by Robin Hobb was an anomaly; a massive drop in quality from Hobb's two previous (and very popular) series in the same fantasy universe, Realm of the Elderlings.
I never thought I would rate a Robin Hobb book below 3 stars, let alone give one of her books a 1.5 star rating. Here are my ways to fix the book:
It should have been a duology, not a quartet
This is what was originally planned by Hobb, but by editorial decision, the story was split up into four books, not two—and it shows. In each book, the pacing is all off, the climax is rushed, happening too soon, too slowly, or not at all.
Changing the protagonists
Thymara and Alise are placed as the heroes of the story, however, by the fourth book, they are pushed aside by with no function within the plot and no agency to influence the events around them. By the third and fourth book, Alise is content with her place in Kelsingra and her romance with Leftrin. Thymara spends four books stuck in a love triangle, and a weird conflict with Tellator/Amarinda personalities trying to take over her and one of her lovers. Thymara and Alise would have made very interesting side characters, but do not function well as the protagonists.
The real hero of the plot should have always been Selden, along with Malta and Reyn. This would have made sense as the Liveship Trader series leaves us with so many questions regarding the future of these three important characters.
Selden's character journey is very compelling, and we could have had a great insight into the politics of the world.
Likewise, Malta and Reyn could have served a very interesting role as the new "King and Queen" of the dragons (abandoned by Tintaglia, now King and Queen to a ruined city, full of bickering teenagers and deformed dragons).
Changing the antagonists
With uncompelling heroes, we are always faced with uncompelling villains. Hobb abandoned her trademark "grey" villains and heroes for paper-cutout, one-dimensional characters.
The Chalcedean (especially the Duke) were uninteresting and un-menacing. He is introduced in the fourth book, and is killed off as quick as he is introduced.
Hest, as a villain, was similarly uninteresting and underwhelming. I felt misled by the way Hobb wrote Hest. I expected Hest to change and grow (as all Hobb's villains do). Instead, he learns nothing, then (spoiler) dies like a piece of discarded trash, his death and existence meaningless and passing by unrecognised by the heroes.
With Selden as the hero, we could have built the Duke up as a great villain. The Chalcedean (as in the actually assassin characters) was scary, but as he only threatened Hest (who we didn't care about) his menace didn't matter. Changing The Chalcedean's attentions towards Malta and Reyn (assuming the two played a larger role in the books) more specifically would have been a much better choice.
Refocus the conflict
The major conflict in the book is romantic conflict. We get the "everyone finds someone to pair off with" cliche, and the "conflict because characters are oblivious to sex and sexuality" cliche.
The conflict should have been about the threat of the Chalcedeans and the tension between the Rain Wilds, the Tattooed, and Kelsingra.
When the conflict in a story isn't working, this usually means there was a poor choice in the hero and/or villains. Changing the heroes and villains would have solved this problem.
Reduce the POVs
Here are the POVs I can remember: Thymara, Alise Leftrin, Sedric, Tats, Hest, Selden, Malta, Reyn, Sintara, Tintaglia, The Duke (+ bird keepers letters, with a few written by Keffria and Jani). This is just WAY too many. I honestly have to say I skimmed, or even totally skipped, some of the bird keeper letters.