>>804525
This actually has an extremely good explanation:
F/SN uses a point system for your relationships. HF Normal is the ending you get if you have sufficient points for Sakura, but insufficient points for Illya. Upon completing this ending, Shirou saves Sakura, and then walks towards the Grail. He sees something crumpled on the ground but doesn't recognize it. That something is Kirei - though he can't tell at the time. At this point, he advances to the Grail, traces Excalibur Morgan, and uses it to take everything down.
If you have enough points from Illya, it's different: When Shirou starts approaching the Grail, Kirei is still alive, and stands in the way. This leads to the two of them fighting, while Illya approaches from behind, and helps Zouken pass on as she does so. The change in time-frame means that by the time the barely-living Shirou manages to crawl up to the Grail, Illya is there to intervene.
However, because of the way the game progression works, if you get the True Ending, it's essentially impossible to get the Normal Ending without going back a huge section of the way through. Thus, even after Kirei dies, you still get the prompt where it gives you the option to view the Normal Ending. This is not the intended progression of scenes, but something which is done for the benefit of the user.
As far as the ending being a Deus Ex Machina: It is very close by definition. However, it is thematically appropriate. One of the huge points that gets made in the story for all of the parts leading up to it is that Sakura living or dying doesn't really matter to her: it's Shirou coming back that's the important part. It's something Rider reminds him of before she departs. In the Normal End, he consigns himself to that fact, and sort of brushes the importance of his own life aside. The True End differs: Following his match with Kirei, specifically in All the Good in This Life, he realizes that he has a reason to keep fighting, and a reason to live. Hence the reason why the text prompt for HF True asks "there must be another way."
One of the things Nasu has written a lot about since KnK is the matter of sins and the bearing of those sins. The HF Normal set-up is meant to mirror KnK: the sinner (Sakura/Shiki) whose burdens are taken on by the messianic archetype (Shirou/Mikiya). The difference here is that while Mikiya is "pure", Shirou is not: the only thing he can do is destroy the Grail. The HF True end has Illya, the actual "pure" person (though perhaps not innocent), take up the mantle, actually shut the gate, and properly bear "All the Evils of the World".
>>804515
>Book
I mean, you can say it makes more sense, but it really doesn't. Shinji's a fucking retard and a confirmed braggart who uses half-truths to inflate himself, as shown in literally his first appearance. He has no work ethic, and takes advantage of Shirou or others constantly to make up for that. He can say whatever he wants, but it's established early on that he's full of shit when he talks. It's a bigger plot hole for him to have done anything on his own.
>Shit-Bag
That goes both ways: Shinji is envious and spiteful towards Sakura for having what he doesn't: Shirou, magic circuits, receiving magical instruction, etc. There are only two people in the story he's like that to so overtly - Shirou and Sakura; and later on Rin, after she rejects him.
>Thematic Whiplash / Progression
That is how it works. Each route builds off of what you learn from the one before it. HF makes a lot less sense if you don't go through UBW - literally every scene with Archer, just to give an example. The story keeps building along, and I can't think of a single solid argument that could be made to justify reading HF before UBW. In any case, the biggest argument most people have against HF isn't thematic, it's "muh cooking" or "muh wormslut".
>>804548
Oh look, it's the faggot who considers himself the master of Japanese literature.