Having been flying the airplane for the last 6 years, I agree 100%. It would be fine on a slower moving, lower altitude aircraft, but it just doesn't have enough range/power to be useful when you really need it.
Forget getting returns on anything but the biggest, nastiest of storms, and during the seasonal transition with the low freezing level you might as well leave it off. I know I've gotten radar envy on the commute home and watching the Airbus/737 paint every little thing thats out there.
As for the worst weather, my experience is limited to north America, so I really can't say. Everywhere east of the rockies sure does seem to get a lot of variety though, from blizzards to tornadoes.