Look at that:
...and now tell me how comes Opportunity weighs 530kg and Curiosity 900kg.
It looks, like by volume, Curiosity is good 4x larger, if not more. Plus it contains heavyweight RTGs, its chassis/frame is much thicker, in short it looks like way more than twice the weight. Meanwhile, it's only 70% heavier.
What properties, construction solutions, mass savings allowed such weight savings in a construction so much bigger?