I think most of us simply exepct the writer to respect the rules that he has himself established, all we ask for is consistency and coherence.
What rule did Kishi break specifically in this chapter?
1.Bringing back dead characters? He has done it so many times before.
2.Giving sudden power-ups? This is pretty much his storywriting
3.Bringing in spirits from the other world? He brought Rin's spirit couple of chapters ago.
4.Letting Kakashi get back the Sharingan? I' m pretty sure everyone expected Kakashi to get it back sooner or later. Sharingan for Kakashi is like how thai jutsu is for Gai. Expecting Kakashi to become a different kind of ninja now would be like expecting Gai to become an expert in genjutsu/ninjutsu.
Kishimoto has been consistently using asspulls since the very first chapters. That's how his story-writing has been. So he was being pretty coherent as usual this chapter. He has done worse asspulls than this chapters. Why the surprise and outrage now?