You are not the only person who thinks like that. I'm on my second Stinger and I've completed week-long trips in both of them. With only two of us, the "cavernous hatch" requires a shoehorn to get our stuff in it, and even then some of it has to go in the rear floorboard.
The trip we just completed in my GT2 involved one medium-sized and one carry-on-sized suitcase, two skinny soft cases designed for takedown carbines, a small range bag, and a GI ammo can. Mama's overnight bag and little Igloo cooler had to be wedged behind the seats, and our jackets and miscellaneous stuff piled in the back seats.
To make it worse, we had to take another small case (15"w x15"d x 12"h) with us to deliver to a friend, and I damn near couldn't find any place for it. As it was, I had to try several configurations to fit it all in. The swooping roofline at the rear and the high floorboard severely limit the height of anything toward the ass-end of the hatch area.
As a GT, which supposedly means a car to travel vast distances at speed and in comfort, the Stinger fails. Between the small gas tank and the smallish and ill-shaped cargo space, it's better suited to short trips. And then, only two people. I can't imagine even trying to take along a small child or two.