One of the factors (in this case with a static departure) so pointedly obvious from the ATSB's animation is the typical small spread of IAS between "still under control" and "lost it" - it can all happen in the space of several knots and can be very dramatic as shown in the animation.
This phenomenon ought to be in the forefront of everyone's mind when playing in the asymmetric sandpit at or near the real Vmc for the day.
It brings a tear to the eye to recall a fatal (in which I was involved subsequently) which was a near mirror image to the present flight path - while the precipitating circumstances differed, the sequence and results were the same (albeit with a full load of passengers). That particular Type was not quite as dramatic as the present case, exhibiting a significant steady yaw prior to departure .. but the end result was the same.
At the expense of repeating oneself, Vmc is test pilot territory and one ought to maintain a comfortably wide margin from it for routine training operations.