what's the point of installing a fuel dump system on a twin engine jet if not to dump down to landing weight?
For FAA certification, the airplane must meet the requirement of FAR 25.1001. It starts with:
"(a) A fuel jettisoning system must be installed on each airplane unless it is shown that the airplane meets the climb requirements of §§25.119 and 25.121(d) at maximum takeoff weight, less the actual or computed weight of fuel necessary for a 15-minute flight comprised of a takeoff, go-around, and landing at the airport of departure with the airplane configuration, speed, power, and thrust the same as that used in meeting the applicable takeoff, approach, and landing climb performance requirements of this part."