Jute and Reuth felt close to useless. Not nearly as useless as the army marching into the jungle in Blood and Bone. Jute and Reuth advanced the plot from their point of view. But they themselves felt useless. Reuth was basically there to make sure the Crimson Guard got through the straights.
Jute was there to play the audience as each barely concealed plot point was revealed and he just sat there asking point blank questions he should have already known the answers to. The sorceress is a Jaghut! Cartheron is working for the Empire! Malle trained Claws! The Empire is setting up a client state! The Crimson Guard are kinda T'Lan! Ok, Jute wasn't there for that one, but if you should have guessed that one by the time the Guard went through the straights and the ice was attacking just them.
I am a little tired of the pronoun game as a manner of plot concealment, seems lazy to me. It's fine if it's a conversation between two characters and that's how they normally would have talked and the audience is just listening in. But there were a lot of times, especially when Cowl was being coy, where Shimmer should have just shaked the shit out of him.
The path of the T'Lan Imass makes no sense. They start in the bone peninsula since they kill Yrkki, the guardian of the bone bridge. But then they march south, killing everyone along the sea of dread?