There can be a lot of difference between cars of the very same make and model. Trucks too. For years I have bought the very same car (always used…I’m cheap…but a long time ago, a partner and I bought the very same car at the very same time). No matter how much they’re serviced, some just get better mileage than others. It’s not always predictable.
Another truck defense. I don’t know what kind of terrain you travel on, but there is no possibility at all of hauling a trailer behind a small vehicle through some terrain that a full size pickup (especially 4wd) will take in stride. Seen broken axles on some of those light vehicles on rough ground, too.
Where I live, much of the ground is really steep. Takes some serious horsepower to pull a load up some of them. Going downhill pulling anything on rough ground is tricky too.
This makes me think of earthmoving equipment. I have a Bobcat 250, and I can move dirt, gravel, rocks, whatever. But compared to a D7 Cat, it’s like digging with a spoon. Some things just require more power and, yes, more fuel consumption per minute. But that D7 will use less fuel on a big job than I will use in my 250.