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. IyengarBackbends are to be felt more than expressed. The other postures can be expressed and then felt. Like in meditation each person has to feel backbends.
B.K.S. IyengarI am old, and death inevitably approaches. But both birth and death are beyond the will of a human being. They are not my domain. I do not think about it. Yoga has taught me to think of only working to live a useful life...I will never stop learning, and it have tried to share some lessons with you. I do pray that my ending will be your beginning. The great rewards and the countless blessings of a life spent following the Inward Journey await you.
B.K.S. Iyengar