Where did you get that hummer models got 7mpg?
My h3 on 35's got 15, my h2 on 40" super swampers got 12.
A diesel conversion h2 can get 20-25mpg.
the original non turbo h1 gets about 12, the turbo diesel Z block gets about 15, and the cast iron turbo F block gets about 18.
Anyway, fuel economy only paints a small part of the picture anyway, here's why:
Combine those hummer fuel economy numbers with the amount built and sold and then compare it to something insanely popular like the Ford F-150 which has just surpassed 250,000 units sold in 2016. 2015 total f150 sales were above 700,000 units. That's in a single year.
The best sales year that hummer had was 2003 and they sold a grand total of about 34,000 units. That's literally 20x less sales numbers. Which means that every f150 you see is putting out over 20x more pollutants than the H2, which made me scratch my head a little when hummer got so much grief for fuel economy based upon little fact and a lot of emotional response.