I agree with your review.

I too am disappointed with how 'simple' thrawn is portrayed in the Rebels series. It doesnt do him the justice he deserves.

Personally if zahn didnt write it, than its not real thrawn canon in my mind. Im not interested in how others have written his character. Its zahn's character and to me only he can write him in the manner befitting his genious.

I just finished reading the sequel to that book Thrawn Alliances. In my mind the first one is better but its still worth reading. I found the book by Timothy zahn 'Choices of One' to be excellent and actually better than the book Thrawn. It reminds me of the first three books zahn wrote for star wars (heir to the empire etc) its got chewy, han, luke, jade and of course thrawn in all his brilliance. I recommend it if you liked Thrawn.