The Hummer H2 was actually bigger than the Chevy Tahoe, GMC Yukon, and Cadillac Escalade. It was even closer to the Suburban 1500, Yukon 1500 XL, and Escalade ESV (but not the 2500 series SUVs) in terms of overall size.
The reason why Hummer made it "seem" smaller (at 189" long, 203" with the rear spare tire) is because they wanted to make it look more "appropriate" for the European market.