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!
When they 'lean in' they can counter the force; oppose it. You would feel 'resistance' build up. When they deflect, they lose posture, do not control distance any longer.
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)
No sir, nice try, but no cookie. Perhaps I am just ignorant stubborn, whatever.
Mind you, the exercises are valuable and have their merit, but no more than striking a boken a hundred times.
Well, look at the attached image, feet are still parallel, but independent sides of the body have formed structurally sounded force bridges in each direction. Central axis is still even vertical. No leaning, no loss of posture. But forces are no longer going where we would have otherwise expected. And this is just external. And this is from Greco-Roman wrestling (not what you were thinking
). As I said, imagination about setup.
There are other reasons to turn stance slightly sideways, that have nothing to do with balance. Making a smaller target for strikes. But at the same time, you trade the opportunity of having equal distance to launch an attack from either side. I find myself using either to taste.