Captain Windsock
Thankyou for your concern but don't worry I certainly do not rely on level restrictions to provide separation, they purely assist in setting up separation. So hopefully I'll be Red Square free for a while longer.
Think Rate
As for your analogy of flight levels and direct routings, it is different.
If an a/c is told to route direct to abc by controller A then after frequency change is told to route dirct to DEF thus missing out ABC it is not the same as:
A\c descending FL130 level GWC from controller A then after frequency change told to descend FL120 by B, will still obviously pass through FL130 on the way to FL120, unlike the different routing instructions.
I totally agree with the previous pilot who said that when given subsequent descent clearance, the descent rate will remain the same therefore satisfying the previous level restriction