@fsb5 You are right, I just realized its too much for a human to understand the concept behind the throne. At first I think it can work if:
1. the user is a mage
2. already learn the concept behind the holy grail war and servant summoning, especially about prana
but yeah, its still too much because if any mage can truly understand the concept, they basically have holy grail in their hand.
I just based it if the user make an appearance in holy grail war. Which means there are 12 enemies (or 14 if the user treated like Gilgamesh) and because holy grail war is basically a battle royale, you can use certain tactic to win.
Btw you dont denied that the user can kill NP and because NP is basically a trump card for every servant and use huge energy, if can you seal it you gain huge advantage.
But like you explained, it depend on how the NP work too, I think its pretty deadly for one shot one kill type skill or regeneration type skill like Excalibur or Hecrates multiple lives, but a bit weak againts low cost many attack type skill like Shirou Unlimited Blades Work, because the user is only human, and even though Shirou swords can be considered a normal sword, it can still hit a fatal wound.
Now I want to see Ryougi Shiki made a debut in Fate Stay Night, I want to see her sliced Excalibur & Gae Bolg in two, one hitted Hecrates, and canceled Medea ancient magics. Maybe after that we will see the first time every master work together in holy grail war.