No sir. Decreasing the durations is not a good balancing act.
Look at all the previous nerfs to CC. Want to know why flesh to stone is popular? They nerfed everything else. Charms went down this summer. Back in the orchard and GH many CC spells were countered with blanket immunites and that tactic continued. (That is turbine continued to pass out blanket immunies to the mobs in subsequents content releases.)
And don't nerf it, by hiding under the "we're helping the players" guise again either. This past summer grazing hits were added to help the players, really it helped mobs hit high AC players so that mez's could be applied during DAs. It was not to help players. We were not having trouble hitting.
In the same mod we got auto regen of stat and level damage. We didn't need this. In fact I don't like having it. I'd rather we just travel with someone who can fix it or carry the appropriate resources ourselves. This change was a step down the easy button road for people who don't like to be prepared and a nerf for people who use tactics other that "kill it all." No more CC, no more incapicitating mobs either???
This is simply one more (or maybe several) step(s) down the easy button road. I don't want curse to wear off. I don't want flesh to stone to wear off. I'll drink a pot. I'll use break enchantment. I'll find someone I can pay to remove the curse. Or I'll wait around until I roll a 20 and save from the stone.
Want an alteranate solution?
Stop letting the mobs spam cast. If I cast hold monster and saw the another mob toss break enchantment and free the first I'd think that was awesome AI. When it did it a second time I'd stop using that spell until the caster was dead. The current AI just keeps spamming the same spell. I was cursed multiple times by the same caster as I waded through his minions trying to get to him. I kept drinking curse pots and he kept casting the same (non-damaging) spell. Why is he not smart enough to change to a new spell?
Now I know my example is a little different, but I feel the solution lies, at least partially, in the AI.
The other part (which my be easier to do) is pretty much what Mad said.
1. Don't reapply the same affect while it is already active.
2. Brief immunity to the affect when it wears off. (1-2 seconds) I did mean brief. Enough time to run or cast a spell.
In addition to what was said in Mad's post:
3. Fix the air elementals separately. Many people have posted good ideas. I think one was about making them switch out of their whirly mode. If that's true to DnD and stops the knock downs while they make a different kind of attack, I think that would be a step in the right direction.
4. Add variety to mob actions. I like the minotaurs. They do all kinds of stuff. The shaman's will cast, swing weapons and charge. It seems like a pretty balanced blend of attacks. I have to defend against each in a different way and I have to pay attention to what they are doing. That is awesome. Make more mobs act that way.
4a. dogs for example should do more than just spam trip.