Very false, since they're *very* likely to put a card on top of their library that they can use right away. You'd have to combine it with some sort of at-will milling, like Thought Scour.

Scheming Symmetry only makes sense if the card you're tutoring for does so much for your gameplan that it doesn't matter what they search for, you'll still be on top afterwards. Generally you want to combine it with some sort of cantrip or draw spell, so you don't have to wait a turn to use it. Doomfall is a card that doesn't further any gameplan of your own, and it doesn't draw a card.