Your engine provides the same power, and the same actual powerband, no matter what gear you're in. The transmission influences how it is expressed to the rider. At your engine's lowest gear, the transmission provides the highest mechanical advantage, and thus the widest apparent powerband. That's good for acceleration—race performance, riding uphill, and getting out of trouble. But at higher gears, you don't need much torque to keep moving, as Newton's first law will tell you. The apparent powerbands may seem narrower, but the higher gears will make your bike happier and less frantic at higher speeds.