Yijinjing was officially recognized as the work of a Taoist named Tiantai Zi Ning in Ming Dynasty. It is a Taoist method of cultivating qi, aiming at pursuing immortality through cultivating qi. The contents in this book are basically Taoist words and contents.
Yijinjing talks about the methods of massage, guidance and breathing, which means change. Tendons are bones and muscles, and Yijinjing is to change your own bones and muscles, and to get through the internal forces of the whole body through breathing and breathing. This kind of internal strength is generally found in Taoist theories and works, but some scholars believe that Yijinjing is a Buddhist achievement method and was created by the founder of Dharma. However, whether it is the Yijinjing of Taoism or the Yijinjing of Shaolin Temple, its content and theory are mainly based on Taoist scholarship.
As for why people generally think that Yijinjing is superior martial arts, I think it may be because there was a deviation when this book was circulated. The idea emphasized in Yijinjing is that no matter what kind of martial arts you learn, if you use Yijinjing with breathing and then get through the whole body meridians, you can give full play to the power of all kinds of martial arts, so it gradually became the very powerful martial arts of Yijinjing when it spread.
In reality, if you learn the breathing and massage methods in Yijinjing, you should be able to achieve a physical quality, and the Taoist method of nourishing the heart also has a positive effect on a person's mental health.