Sorcerers got the short end of the stick when Forget was taken for Savant reasons and we got corrupt essence instead.
Forget stopped spells from being prepped, Corrupt Essence stops spells from being cast. Obviously Forget is much more useful as, after the duration is over, the critter still needs to prep a spell before they can cast. With Corrupt Essence the critter can prep during the duration and cast the spell the instant it is over.
What was gained by the lessening of functionality? Nothing.
I would ask that the duration of this spell be increased from 15 seconds to 30 seconds (or 25) to make up for the usefulness we lost when it was taken by Savants. Or, increase the base duration to 20 seconds with an increase of 1 second for each 10 ranks of mana control skill.