To be fair Dingobloo the Xel'Naga have been a major part of the lore since vanilla Starcraft, and with Samir Duran in BW you just knew it was going to come up in the future. Kerrigan going human and back served two important purposes: 1) Duran/Narud needed to suck all her power into the xel'naga artifact so he could resurrect his dead master (Amon, or w/e his name is I forget, the dark voice). And 2) it allowed Kerrigan to regain her power without the corruption from Amon, allowing her to lead the swarm of her own will, a fundamental change to the zerg.
I will say though I'm a bit confused at how they claim now that the fallen Xel'Naga was responsible for evolving the zerg, I thought all the Xel'Naga did that together. Unless they mean he corrupted their evolution without the others knowing.
At the end of the day though I can accept Kerrigan's decisions and motivations (even though I miss a purely animalistic primal evil zerg like the old days). The main issue I had was Raynor's progression from "You and me are over" to "See ya darl" as she floats into the sky. It makes sense for him to put aside his differences to help her destroy Mengsk, but I really thought he would have more questions before letting her go away to do her thing.
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