Regardless of how much your bike and panniers weigh, the rider decides how much power to put out. 150 watts, 200 watts, 250 watts.
Varying the weight will change the gearing needed, and the elapsed time for a given distance, but putting out 200 watts with rocks, is the same as 200 watts without rocks.

In extreme cases, adding a lot of weight while climbing, will effectively make the climb "longer" because it takes more time to compete, so if that's the goal, then I guess adding weight would work.