It's not the weight! Forget about weight completely. It's the stiff casing and treads. The same thing that makes it a tough offroad tire makes it suck fuel. If you need the toughness offroad and mud traction, then fine... else it is not your best bet.That was actually the thread that got me turned onto the ST Maxx. As you mention, the weight is pretty high with those tires though. My Tundra already gets abysmal fuel economy. Did you find much of a loss with the heavy tires?
IMO most ATs are placebo tires. You need enough voids to clear mud else you might as well be on street tread. They aren't doing anything for you on gravel, dirt, or sand. If they have a more durable casing, then that's going to cause a harsher ride and suck fuel. No free lunch.
For your stated use (road and a little gravel, no mud) you'd be better off with street oriented tread for sure. Low load P tires will give you the best ride and fuel mileage.