Xue Sheng
All weight is underside
OK let me put this way. Push hands can be be whatever, but it original purpose to let practitioners to develop skills. Wrestling and any other kind of derivative of push hands are neither free fighting nor traditional training method, it's more like a modern sport.
Traditional taiji fight is about maiming an opponent. It means anything goes. As any martial arts taiji has its own "game". The problem is not many people in the modern world aware or knowledgeable enough to go beyond push hands.
Good point, not many in taiji these days realize that applications to things like (扇通背) (shan4 tong1 bei4) "Fan Through the Back", can break an elbow (you should see the look on students faces when I tell them some of the Dao applications). Once was at a seminar with Dr. John Painter and he talked about many missing the point of push hands and how things like "Competition push hands" are completely missing the point and ruining push hands training. Truth be known, I agree with him. If someone takes the time to look at the applications to many of the postures in taijiquan they are brutal, many for maiming the other guy.
The push hands I have trained and do is trained in various levels; stationary, moving, 3 step, 1 step, following, free style. And at higher levels (free style) you get into applications However it is more to using the applications properly, not forcing or muscling it. It is, like I said, kind of like Aikido Randori, and like Randori, it is still not fighting.
It is through, relaxation and "lightness" ,if you allow me to quote the OP, that you apply taijiquan and it is push hands training that gets you to better understand how this 'relaxation' or 'lightness' (if you will) works for the proper application of taijiquan that so many miss these days and instead go for quicker to learn, more 'powerful looking', more energy intensive, methods like those in Sanda