Yeah, what you're doing here seems more like Gil's "All Seeing Eye" than Saber's instinct. Her instinct allows her to anticipate attacks and know what her opponent is going to do, it doesn't allow her to magically detect things like weapons. Even in battle it doesn't do that, it just gives her a supernatural sense of how to act to get the best possible outcome.
For example, even in battle, Saber wouldn't know what the enemy's weapon was. She'd just know "I need to do this to prevent it harming me". And, even that is not perfect, as Caster's use of Rule Breaker demonstrates.