When I did a Traffic Patrol Course with the police, we had some input from the Transport Research Laboratory, at Thatcham.
They showed us video footage of exactly this problem. When you brake heavily, the weight of the car is pushed forward, over the front wheels. This makes the back of the car lighter, and the front heavier. If you have less tread at the back, it is more likely to let go, particularly in the wet, when aquaplaning is more prevalent. It is therefore always better to have the best to the back, regardless of whether it is front or rear wheel drive. I would stress that this has been proven, and isn't just an opinion.