That's a lot of mass perched up there on top of the fin, near tremendous air loads and vibration from the engines (think reverse thrust). They would shake around, and in the air doing flight manouevres. The DC9 series look bad too, with their very thin airfoil sections and elevators that appear to move independently of their own volition on the ground!
The most efficient part of the VC10 and the 1-11 was their sheer ability to convert fuel more efficiently than anything else directly to sound energy! In the case of the VC10, a little got converted to thrust as well.