I know that the controller should not reduce the speed of the aircraft while the aircraft involved is descend, because it's almost impossible for the pilot to do these two things at the same time
For most jets it IS difficult, but not for the Fokker jets...F100 and F70. We can go down, slow down, turn, whatever you like! I know it surprises ATC sometimes just how quickly we can lose height!
Now gaining that height quickly in the Fokker- that is another matter! ATC, please don't expect us to climb like a Boeing!