While barrel vibration is going to be significant in hold sensitivity, it is the effect it has on the group size at the target which is important and this is also dependent on the pellet reaction to barrel movement.

As the pellet leaves the barrel, when the head leaves the barrel the pellet CG will start to move sideways in the direction of the vibration. However, the rear of the pellet is still held in the barrel and its sideways movement will not be the same as the pellet CG which will cause a yawing rate. If there is one thing diabolo pellets as a design do not like it is yawing rates due to their basic ballistic properties but the result, in terms of group size, will depend on the ballistic properties of each pellet type. The effects can be minimised by trying to match the pellet exit timing to the barrel movement but the pellet reaction to barrel exit conditions will still be important and you could easily end up with a pellet which has ideal timing but lousy ballistic properties giving apparent high sensitivity.

Hence, hold sensitivity will depend on the pellet design as well as what the barrel is doing.