You're not supposed to cap the 2-3 fuel points right outside your base for permanent bonus fuel cheese that the enemy cannot contest. That was never the intent behind this ability.
Stop shooting it at max-range into the fog of war against random targets and you will see better results with a rocket arty that costs 0 fuel
That's a lot of assumptions you are making. I suggest you build a Nebelwerfer and see for yourself. Even direct hits don't kill infantry models and the flame damage only sets in if your opponent doesn't simply move the infantry out of it (not even retreat but move the unit 3 meters). So I stand by it: The Nebenwerfer is shit.