I honestly forgot about those skills.Status ailments like sleep, confuse etc never work on "key" enemies. If it's an enemy you have to kill to move forward then status ailments of that kind aren't going to work on it. You can use the ones that lower resistance to particular elements though, those work OK.
It's a pity there isn't a spell you can use which will actually lower an elemental resistance enough that they'd actually be weak to it.
My point still stands though, particularly with that example I gave.