Regarding Gilgamesh getting taken out by Master Li's first strike.
First of all, the original work mentioned multiple times that Gilgamesh had never taken the Holy Grail War seriously. Even when angry, he still treated the fight with an attitude of "I'll just use a little force to crush this bug." Put simply, no matter how furious he got or how badly he was beaten, he never truly took things seriously from start to finish. He was just messing around.
The many ways he died across the game's various routes were all because he was messing around. Honestly, a lot of people only know Gilgamesh from Fate/Grand Order or the Fourth Holy Grail War, and they actually refuse to acknowledge the Fifth Holy Grail War. That's just baffling—the Fifth Holy Grail War Gilgamesh was the one who truly matched the original setting. Nasu only patched him up a lot later, which is how he ended up with those later stats.
Back to the original question: could the Fourth Holy Grail War's Gilgamesh have been taken out by Master Li's first strike?
The answer is an absolute yes.
The reason is simple. Master Li's Round Mirror A skill provides perfect concealment, hiding both his presence and his figure in an instant. He can even vanish right in front of you, then get behind you and use Thousand Years of Death.
Thanks to this move, he even took Koyanskaya, a Beast Cub, out with a first strike in the game.
And that chapter's story, like Fate/Zero, was written by Urobuchi. So Master Li's abilities could be carried straight over, without even needing to settle things by having characters from different authors fight to see who was stronger.
On top of that, in the official story, Gilgamesh was taken out by a first strike in the Fourth War Singularity.
And the lineup there was Berserker Lancelot and Zhuge Liang. Their ambush was nowhere near as effective as Master Li's, a man with maxed-out expertise in the field.
What's more, Master Li in this book also has the home-field advantage.
So, is it really unreasonable for Gilgamesh to get taken out by a first strike? It's completely reasonable.
So reasonable, in fact, that when I was working on this section of the story, I suddenly realized that if Master Li decided to kill him, Gilgamesh would have to leave the story right away.
So, as a Gilgamesh fan, I still gave him some face and didn't have Master Li kill him outright. I figured that was a way of respecting his standing as the strongest Servant in an ordinary Holy Grail War.
If he'd been ambushed and killed the moment he appeared, just like in the official story, that would've been the textbook example of utter humiliation.
But thinking it over, I suppose it's understandable. After all, the official story had already turned him into such a laughingstock that people could trick him into becoming a battery. Truly the greatest disgrace among Gilgamesh fans.