Backbends 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. IyengarBackbends are not poses meant for expressionism. Backbends are meant to understand the back parts of our bodies. The front body can be seen with the eyes, but the back body can only be felt. That's why I say these are the most advanced postures, where the mind begins to look at the back.
B.K.S. Iyengar