Dan Harden wrote:
"Without peng-jin, there is no taiji."
It's the exact same meaning as Ushiro saying, "No kokyu, no Aikido".
In fact, most western versions of Asian martial arts are mainly external replicas of the techniques (no matter how smoothly done, good timing, etc.). However, we're on the cusp of seeing more and more of these skills returned to the Asian arts. Right now, it looks like Aikido may actually be in the forefront, if things continue.