That's why our team uses long rope belay techniques, not short rope. Of course short rope bottom belay techniques don't work well for long ropes!!
Our belayers all wear a harness and QAS, and have an quick escape route which is downhill fast, so that if a rappeller goes out of control you can quickly get a full 300-400lbs of belay, which is MUCH more than you can achieve by simply pulling down on the rope.