If you OW the prerequisite for a feat, is the feat not usable? I can see the argument either way. The power is cancelled, but still on the dial.

If you Outwit a power...that power is not considered to be present on the dial. Because it is not present on the dial it cannot be used to meet the prerequisite of the Feat. If you cannot meet the prerequisite of the Feat, you cannot use it. (This doesn't mean the Feat is KOd, though.)