In the P85, you can spin the wheels with TC off. I haven't heard of people doing that in the P85D because power is distributed to all four wheels, so it tends to grip the dry pavement.
But it's not distributed to all four wheels - which was my point at the end there. The P85D rear motor is supposed to be exactly the same as the P85 drive motor, and it still only drives the rear wheels.
At low speeds, the battery can deliver far more power than both motors/inverters can take (from videos it looks like the D goes power limited at about 25 mph under current firmware.)
So in principle, the P85D should spin the rear wheels exactly as easily as the P85 does - the front motor adds additional torque and acceleration, but doesn't change anything about the situation at the rear.
That's why I'm still thinking the car is pulling back some power, though it apparently doesn't flash the TC light as some expect it to from other experiences.
Walter