A small car today like the Hyundai Accent makes 138hp at the wheels and weighs over 2500lbs.
The Colt made about 68 hp and weighed 1900lbs.
The Colt would look tiny parked beside the Hyundai.
The Colt did 0-60 in about 12.5 sec
The Hyundai Accent does 0-60 in 9.2 sec.
A lot of the weight comes from safety and comfort/convenience add-ons. And they're built larger because Americans have become larger. And the Suburbans, Hummers, and Expeditions out to squash small cars have gotten much larger.
When you factor in the weight and power increases, efficiency doesn't seem so bad.