Output Adjustment allows you to reduce the max HP of the engine, which also reduces the Torque.
It's easy to think that the Power Restrictor does the same thing, but it doesn't actually reduce the max HP of the engine, it just reduces how much of it you can use, which has less of an impact on Torque.
Try reducing the engine HP to a certain number with the Output Adjustment, and check the Torque. Do the same with the Power Restrictor and you should find you have more Torque available at the same HP.