If you don't use ankle flex to bring you forward then the next joint up the kenetic chain that moves in the forward direction is the hips. (once the knees are straight they, hopefully, don't go further forward! )
When the hips are used 'get forward' all sorts of bad things happen in your skiing.
So I'm sticking with the ankles as the best way to get forward. I.e. Move the COM forward.
Interesting. But I respect your opinion offcourse. How many skiers ski with their leggs fully extended when they are centered? Since the boots have a bit of forward lean in them we are flexed at the ancles, knees and hips as a default. It would be interesting to see a demo of the move you are refering to.