Just a few of my opinions:
Hizdahr zo Loraq was implied to be the leader of the Sons of the Harpy, yes, but imo there were so many clues pointing to him as the leader that I think it was a red herring and the true leader is still out there, if there even is one true "leader" at all.
Also, the brothel and the entire thing with Shireen weren't creations of D&D, just to clarify. Arya and the brothel was revealed in a leaked chapter of Winds of Winter (where it's not Meryn Trent but the guy who killed Lommy, but eh close enough especially since that guy's already dead in the show) and GRRM specifically told D&D to burn Shireen, which was shown in the behind the scenes for this episode. Yep, we've reached critical mass here- the show is ahead of the book at times.
Anyways, while I can't say I've forgiven the Mannis for what he did, I gotta say I understand it. Even if he doesn't have an heir and lots of shit goes down when he dies, it's much better than everyone getting massacred by the White Walkers, which is why Melisandre is even with him in the first place, remember- he's the only one who can stop them, as no one else but Jon and the men of the Night's Watch give half a crap about them.