Really? So if he stands in front of me, feet apart (shoulder width) and I push him backwards he can withstand that force without stepping backwards, without losing posture? Seriously? SHOW ME!
Yes, that is the goal. It's not even that difficult. (I'm pretty much a beginner at IS stuff, and I can do it.)
If all that works so well why does every single martial art place one foot in front of the other (boxing, kendo, fencing, karate, kyodo, kungfu, wrestling, mu tai, bagua). The only one I can think of that does not do so is sumo, at least when they start. But even then look carefully what happens on contact (bodies turned, arms put rotating force in opponent)
Once you're stable in a shoulder-width square stance, being stable in hamni is relatively easy. Then the challenge becomes keeping that stability as you move.