Why not let the crewman land in the seat?
An ejection seat is a large object which has a certain mass. If the crewman was to descend in the seat, the parachute would have to be larger, or there would have to be another deceleration device to make the landing force acceptable to the human occupant. This is the case in terms of ejection capsules such as the B-58 capsule, and the XB-70 capsule, as well as the F-111 family crew module. For an open seat, the problem is larger as the seat would make landing hazardous to the crewman. In water the seat would act as an anchor and drag him under. The capsules and modules mentioned used flotation devices to prevent this.
