Nothing is more essential to Kung Fu than stance training. The meaning of the training will change as you progress but it can never be done too much. Even in Northern Long Fist high kicking is just a stage of training. In recent years high kicks have been confused with Beijing Opera kicks so now many practitioners of martial arts don't even know the postural differences. Flexibility is important but the flexibility of Kung Fu is very different from that of a dancer.
High kicks are an important stage for a beginning martial artist to go through.
Kung Fu has many skills. They vary somewhat from style to style. Most of them start simple, defending one's centerline, kicking without losing balance. The skills must be practiced steadfastly and refined throughout the lifetime of the martial artist. But of course.