Volumen Hyragyrum requires mystic circuit activation--it's how Kiritsugu beat it--but is an automatic defence. Tokiomi wins because his staff makes Rin's jewels look like the child's toys they are.

Er, I see two huge problems: one, those pure eyes.[hider=Eye Problem]The ability to outright rewind time to view the past would either fall under the Second Magic (it's noted that time travel falls under the operation of parallel dimensions--hence why it [i]can[/i] alter the past by creating a new dimension--or the Fifth Magic (because that's its whole schtick, only it doesn't have the 'alternate dimensions' bit so Aoko has to fudge things to mess with what's already happened), which isn't quite the same as the Pure Eyes deal of 'seeing things that are normally unseen'.

The other part is how much use that grants [i]specifically[/i] in the context of a grail war. So, with no prana investment (since pure eyes, not mystic eyes), if he can get into somewhere a Master has been alone, or where they're summoned, or their house... then he can gather information with absolutely no effort, difficulty, or means of stopping him.[/hider]

The other: the counterspell thing wouldn't really work, for the same reason that a magus is incredibly hard to mind control compared to a normal human (also, I guess, the reason dragons and Saber have Magic Resistance): prana resists prana. Trying to lock down magic circuits would probably take [i]more[/i] effort than just disabling them by force, as you're trying to put a spell in place against something that is constantly, actively resisting. Kiritsugu's bullets can do it because of a combination of his Origin, and the fact they work on a more physical level, and reconfigure the magic circuits into being nonfunctional.