Current MMOs seem to have a complete disregard for Crowd Control to begin with. Tanks and Healers are FAR too powerful for their own good.

I'm personally a sleep-a-holic. I love Crowd Control. But I also come from the "old school" where failed crowd control meant a party wipe. Being able to tank 2 or 3 mobs at once made you a God among Men. And that's the origin of the design flaw. Crowd Control was there to keep your Tank from being overwhelmed by incoming multiple sources of damage. The moment where you negate that by giving them enough defense to laugh in the face of patrols or packs of mobs, is the moment you have cut any need for crowd control.

You also cut any need for tactics beyond the basics.

The funny thing though is, the content is actually designed to be balanced around Crowd Control. Take AK for instance. While most of the mobs can't be put to sleep, those times have less incoming damage than the ones that can! The 3 hipogryphs in the front room cant be slept, but they get killed with nary a thought. However the room with the one demon beast and the two houndlights? There's a marked increase in how much damage your tanks going to take. It's no surprise that sleep works on the hounds, but not the hipogryphs.

"But it's unfair! Not every group is going to have CC!" There's actually a lot more CC in the game than people seem to realize. White Mage and Black Mage have sleep sure. But there's also other forms of Crowd Control out there as well.
Summoners have an off tank to hold an add with no threat to the group.
Archers can Kite a melee mob while it's buddies are taken out normally. Not to mention Rooting.
And let's not forget that Tanking, by it's nature, is a form of crowd control.

The tools are there. The Need is not. As long as the players CAN ignore complicated tactics they WILL ignore complicated tactics. And currently, the reason that they CAN ignore complicated tactics is because handling 3 mobs at once is usually not a problem for a tank/healer combination. (3 being the normal group of mobs you encounter, Stone Vigil and Haukke have rooms with more and suddenly things become much different).

But there's another factor involved. CC only really comes into play on trash, and we call it "trash" for a reason. I can only think of 1 or two places where Sleep is in play on a boss encounter (Brayflox, Drake boss comes to mind). So in order to really make CC worth it we'd need to make "Trash" not be....well....."trash"! Which really only brings me back to Haukke and Stone Vigil with their optional rooms. So obviously, I'm of two minds on the subject.

To take it back to Repose, when asked about it I usually go with this canned answer "Repose healed 100% of the damage you didn't take."