For example, if the gear wrench is for 3600Nm type, the gear ratio is about 15 times. In other words, rotate the input shaft 15 times, the output shaft makes only one turn.
You use a hand torque wrench there, but since one swing of the handle at best is 30°approx, in order to rotate the output force shaft one turn, the handle has to be swung 180 times. If you try to rotate the output shaft twice, it comes to 360 swings.
In addition, the input torque needs about 370Nm at maximum for the purpose. If the torque-wrench is 60cm length, you need arm- power of 62kg on the handle. Can you repeat it contineousely 360 times? You might not die with this heavy work, but get pretty exhausted.