The real fix would be to make it non-doctrinal - add something usefull to the doctrine. The WC51 is great, but mediocre for a call in unit. The unit would add alot to the USF early game.
The problem with that is m20 just superior in like every way. It's literally only viable very early. So not only would they have to cut the fuel, they would need the stats to reflect the cost.