I agree with the author's sentiment about cutting the fluff being good for the show, but strongly disagree with his seeming dislike for the characters in the books. I doubt that the author has re-read AFFC/ADWD. Once you get past the strong urge to rush through the books to see what happens next to the "main" characters, these new "side" characters really come to life. In particular, I didn't care for all the Greyjoy shyt on my first read, but on re-read I am now a Victarion stan.
As far as Arianne goes @TheGreatShowtime she plays a bigger role than just the Myrcella shyt. Not sure if you have read the Winds of Winter chapters yet:
She is leaving to meet Aegon and will be making the call whether Dorne goes to war. Speculation assumes too that she is going to try and seduce Aegon for marriage
I haven't but I know Doran is trying to set her up with Aegon as it was said in ADWD. They could always introduce her later too.