Not being funny (I fly A330 by the way), but isn't it interesting that no other ATC agency has reported problems with this? UAE isn't the only area with level restrictions. Many times coming into all kinds of places, we have been level pegging with 767's etc, and there is no difference in the way ATC handles us.
As has been stated, the A330 will not go down and slow down without a lot of speedbrake, and if you don't modify the descent speed, it will carry out a very slow, but very efficient descent. You can't have it both ways! Maybe a bit more flexibility from both sides is the key here?
Also, about 767's climbing faster than 330's - not much in it really, but please remember that the 330 will be going to a higher level and will in all probability be cruising faster than the 767. I'm not getting into the A vs. B debate - that's just how it is.