Notice the 1.125" width of the belts on Buell sport bikes. Belts hold up just fine to pretty excessive power. The 4 inch belts on custom bikes are just for looks.
Lube on the rollers penetrates to the bushing to roller interface, an important area to lube. The bushing to pin interface is where lube is sealed in.
How is it that the belts on my dyna (84 hp and 95 ft. lbs of torque) and the XR1200 (86 hp) manage to hold up just fine but would not hold up to the mighty 63 hp or so of the Wee Strom?