Although it may appear like a slow combination, combination it is not.
With combinations of attacks where the last one in the series hit a weak essential pressure point in the right amount of force and stops the opponent completely or buys you few split seconds of time, the training drill design takes the assumption that you need to chase the opponent fast without hesitation as he is retreating and also that the first attempt will not reach its destination.
If it did reach its destination, the impact of the strike will naturally slow down the execution of the following attack. This nature of physical phenomena calls for at least two separate training drills for that purpose.
Sparring would be an invaluable step in mastering spontaneous application of material learned. Prior to that step, students need to learn to control their strikes and kicks properly so that while providing realistic taste of what happens in a fight, they do not cause great injury to students!