So the interesting thing is that a wider stance can actually be LESS stable if you do not have 50/50 weight distribution. Did I just say that?
Take a stool that is small in size with the 4 legs close together. chop off the legs from one side and the stool will fall over, but it will teeter over slowly.
Take a long bench and chop off the legs from one end and that end will drop very fast. wider is LESS stable unless you are standing on both legs. If you're wide and you're manipulating lateral balance to transition between turns, then the wider stance creates instability, not stability.
Wider has many disadvantages except for when you truly desire to be standing pretty equally on both skis, then perhaps wider is more stable. But is that the kind of stability you want most of the time? Do you want to block yourself from moving laterally across your skis? No I don't think so. And 50/50 is hardly ever the desirable case. I have never understand this obsession over a wider stance. Doesn't make any sense with the way skiing works. Feet locked together is not good, but if there is independent foot action, there is nothing at all less stable about a narrow stance under most normal ski turn situations and if you are primarily standing on one ski, then the narrower the stance the more stable you will be!
If you hang from a pull up bar and let your legs hang freely, whatever width that is, is probably most ideal for mobility in the joints, and that width is a lot narrower then most people think. its not hip width or shoulder width, its narrower.