The theoretical feasibility of the power output strategy based on rotor cone angle control for ultra-scale downwind wind turbines is studied in this paper via the Open FAST simulation platform. The performance of five cases, namely UW, DW, DWC, DW6, and DW6IC, which have different rotor parameters or control strategies compared with the reference DTU 10 MW wind turbine, are calculated and analyzed. It is found that the downwind rotors have significant advantages in reducing the blade root load. The DW case reduces the peak load at the blade root by 22.54% at the cost of 1.57% annual energy production loss. By extending the length and redesigning the stiffness of the blade, the DW6 case achieves 14.82% reduction in the peak load at the blade root and 1.67% increase in the annual energy production under the same blade weight as that of the UW. The DWC case with rotor cone angle control has the same aerodynamic performance as the DW case with the same blade parameters. However, when the wind speed achieves or exceeds the rated speed, the blade root load decreases at a greater rate with the increasing wind speeds, and achieves minimum load with a wind speed of 16 m/s. Compared with the UW case, the DW6IC case with the improved rotor cone angle control reduces the peak load of the blade root by 22.54%, leading to an increase in annual energy production by 1.12% accordingly.