Having read it in brief, thought has struck me,that if the brakes are applied to stop both wheels spinning on the front, then you are pushing against a front "handbrake"
This is where a centre "diff lock", and not an axle lock would come in, so you would not need to stop the front wheels to avoid the wasted effort going to the spinning wheels.
Having read the vw bit, it would seem I'm thinking right, as it does away with the front/rear axle speed compensation.
Not sure that I have explained what I'm thinking well, as suffering at the moment, as I say, worth looking into.