Yes, flexibility of body and physical perfection for Yogasana is important. However more important is the state of your mind, Meditative mind. Your flexibility might be excellent but if your mind is not attentive, you are merely doing some physical exercise, not Yoga.
B.K.S. IyengarYou know the known, so go a little into the unknown. The mind that is caught up in the known - extended a little beyond reason. The moment you go beyond , you move in the soul. Releasing the bondage of your mind to extend further, reach the unknown a little more. The further you go, you realize that the known is limited and the unknown is vast.
B.K.S. IyengarNot all practitioners can jump to that highest level. They have to climb, step by step from the physical sphere to reach the spiritual sphere. If it is treated as exercise it is not the fault of yoga but of the practitioners.
B.K.S. IyengarAs long as the body is not in perfect health, you think about it, and that prevents you from thinking of the mind. The sound mind is a sound body.
B.K.S. Iyengar