The real question though, why do Nasu has such strong prejudice against Tamamo?
First, Koyanskaya isn't a Tamamo (despite being named as Tamamo Vitch, referencing Tamamo in NP and being exact copy of existing Vitch's concept, up until Tamamo no Mae saying that Vitch is "beautiful and talented secretary"). It's after her calling herself a Tamamo from another world in profile, which was a lie for no reason.
She is not just "not a Tamamo", but also is a nature spirit (elemental) who has no name ("she failed to acquire a name as a Beast, therefore her name is Beast IV: Lost" in the Beast's profile). So, Tamamo Vitch, Koyanskaya, it's all are fake names. HOWEVER, in the origin story it is mentioned she was blessed by Amaterasu, so just why is she not Tamamo?
Second, the weird ascensions of playable Vitch instead of constumes. The 1st ascension of Light, what is even that? The second one of both Koyanskayas are clown/playboy cosplay. The third ones are only reedemable being reference to Amaterasu in a sense.
Third, the weird Taigong Wang shipping for no reason. In the original story, Taigong was a man who was loyal to the Emperor, and when Daji ruined his dynasty, he went to actually defeat Daji. Not to mention, he had two wives. In FGO, he is obsessed with Daji and Tamamos thought they should be his enemies. And Koyanskaya should not even know him if she's not Daji, except she for some reason does.
Fourth, foreshadowing? What is that? Why did Koyanskaya said that Holmes is her Nemesis? Why did she refuse to name Holmes' class in Olympus? What was her deal with Daybit? Nothing being answered, instead please have Fabro Rowan dude who looks like Nrvnsqr (removed from Tsukihime) for no reason and Sion doing 4th wall jokes in main story.
I am rather happy that LB7 is going to be last story by Nasu, and hope that Part 3 would be written by Higashide, Sakurai and Meteo (since LB7 is announced to end on 7th anniversary and the game would continue until 10th at least, I hope Nasu would keep his promise and leave).