One way to look at them is the weight per length. When I do a side by side comparison between the two models you specified, a slightly longer Heritage Glen unit weighs 500 pounds less than the Sabre, slightly shorter.
Generally, those extra pounds are used to build strength and insulation.
Compare similar length models and look at the UVW of each unit.
Mike
2012 Winnebago Impulse Silver 26QP
2005 16.6 Double Eagle
2018 Jeep Wrangler JK
previously Snowbird Campers,
Triple E Motorhome and Fifth Wheel