Problem is it’s not always true. For example, the current 6 cylinder Goldwing has 126HP and 125 ft lb of torque. The SVTC v-twin has 90HP and 126 ft lb of torque.. Given that I have the Ivans Flash tune on my ECM, I’m currently running about 137 ft lb of torque.
Yes, a multi cylinder bike will be smoother but has nothing to do with adding more torque. Torque is what gets the bike moving. Hence it’s more about the gearing than the cylinders.