I think this was something RJ just could not understand all the fuss over. He made a comment in one of the Question of the Week posts that were a feature leading up the release of KoD, in which he spoke rather dismissively of the fates of the Forsaken who did not get sealed up with the Dark One. I don't think he considered the machinations of the Forsaken and the Shadow as big a deal as the readers did. There was another question he blew off in an interview or fan Q&A, asking which of his characters he'd like to have dinner with, replying that he wouldn't like that, because there would be no point to such a conversation, as he controlled every thought in their heads. I think that stuff illustrates something about his mentality, where some of the detail-oriented fans were looking for things that made absolutely no sense to the real appreciation of the story. The important thing to the story, is that Asmodean was removed by the Shadow (I don't think anyone really believed anything else), and Rand had his last mentor figure taken away, just as Lan & Moiraine had left earlier in the book, and the dynamic between him and Nynaeve had just been shown to be completely altered. It was showing that even at his pinnacle of power and badassery, the Shadow could still reach into his inner circle and take people or things away from him, and it happened in Asmodean's first and only PoV showing that he WAS actually loyal to Rand, if not in any particularly likable way. Subsequently, it would lead to Rand's increasing dependence on Taim and everything that followed from that.

Knowing that Graendal was his killer changes nothing in her character arc in subsequent books (though RJ appears to have dropped a hint with her recollection of raiding Sammael's trove after Rand took Illian - suggesting that she has the skills and inclination to infiltrate a place Rand has just conquered, to remove One Power resources from his access), so there was really no value to that information. Once it became such a massive point of interest for the fandom, probably against RJ's expectations, he might not have known how to best handle it, either not wanting to disappoint people with the reveal, not wanting to do so outside the books, not wanting to shoehorn the revelation in there where it did not fit, or any number of other reasons. Heck, common sense would suggest that as long as there were fans interested in the detail, there was an additional motivation to buy the books. It's pretty much a rule for magicians not to reveal how they do their tricks, not just to keep up their professional image and whet appetites, but because it doesn't really make people happy.

It depends what you mean by united. Under a single government or leader, not really. But why would the Pattern care about legislative trivia like that? What was important was a unity of purpose and action, that those who were going to contribute to the fight against the Last Battle had to be pulling together. In that sense, they were united. While I agree the final books did not do a great job of conveying that sense of unity, the inability to get that sort of thing across plagued the Sanderson books.
She only saved Rand's life directly during the Last Battle itself, and was one of the two women supporting him, that enabled him to use Callandor, and wield saidar & saidin there. Remember the importance of them being "as one" and the way the linking process was always described. One of the critical points for Rand was that he be able to trust the women he was linked with. From the first conversation about the reality of men and women linking, way back in tFoH, the role of trust and control was portrayed as significant, including the debates between Sammael, Lanfear, Rahvin and Graendal about their plan to link to capture Rand. Nynaeve was important, because she spent the previous 11 books establishing that she was one of the people Rand could trust the most. She proves it by saving him from Alanna's death, being both smart enough to figure out a problem and motivated to do something about it for Rand's sake. Not even his girlfriends really did as much of their own hook for Rand as did Nynaeve. Cadsuane acted because he was the Dragon Reborn, Moiraine's actions were shaded by her White Tower perceptions, and even the girlfriends' view of him was shaped by his development. Tam was entirely locked into the perception of him as a kid. Nynaeve was the only one who knew him before, and stayed friends with him the same way as he developed.

The degree to which other things were left out might be simply that they were not very important, or that their role was facilitate earlier developments and changes (i.e. Siuan), in spite of perhaps some fans' assumption of exaggerated significance to them.

Finally, we don't know how the Last Battle was really supposed to go, because Sanderson chose to take a top-down view, describing the battle as if the fighting itself was the important thing, or that it rested on the success or failure of certain maneuvers or gambits, when really, the important thing was that everyone contribute to the best of their ability, and give it their all, because it all comes down to how Rand chooses to act in the end. Sanderson gave us those events, but not the sense of their importance or relationship.

Well, there was the bit about her being someone Rand could trust to work the Power with him in Shayol Ghul, and that she was someone who could intervene whom both Egwene and Rand would listen to. Egwene would not have respect for anyone outside of the White Tower, and saw all those people as her lawful subordinates, so she would not listen to Nynaeve or Elayne or Cadsuane arguing for the need to accede to Rand to any degree. Also, it might be that the purpose of her rescue would have been whatever effect RJ planned for it to have on Mat. I heard rumors that Sanderson completely changed Mat's arc, and even if he didn't, Mat was the character he wrote the most poorly, with the least comprehension or understanding of what makes him tick, so it is very likely that Sanderson lost whatever significance the whole episode in Ghenji was supposed to have on him.

I'm actually sort of curious as to what people expected from Moiraine anyway. She wasn't superman, or even all that competent. Her advice to Rand was almost always wrong, ill-informed, short-sighted, and stuck in an outdated paradigm. Most of her plans when she was "in charge" were just variants on "Run" or "Hide". Her most admired accomplishments, killing two of the Forsaken, involved her shooting them in the back while they were fixated on Rand, and immediately being taken out of action. For all her abilities, resources, experience and manipulation skills, she was losing the struggle with Perrin by the time they got to Tear, and then proved how badly she mis-estimated him early in the next book, and was marginalized by Rand well before she gave him her oath, which itself was a sign of her ineffectuality. Moiraine was impressive and daunting only because we saw her through the eyes of kids who didn't know their asses from their elbows about anything outside of their village. By the time they got to their powers and resources on the eve of Tarmon Gaidon, they'd have put the Aes Sedai who was always sneaking out of town with her tail between her leds in a corner to play with dolls while the grown-ups dealt with the problems ahead.