It's only fair to keep the size classes in line.
Let's look at cars actually made in the U.S. by U.S. brands (which leaves out the Cricket, Colt, Fiesta, etc)..
The following were "sub-compact" cars.
Vega, Monza, Chevette, Pinto / Bobcat, Horizon, and the Gremlin / Spirit.
The following were "compact" cars,
Rambler American, Hornet / Concord, Falcon, Comet, Maverick, Fairmont / Zephr, Valiant, Lancer, the post-'62 Dart, Studebaker's Lark, and the Chevy II / Nova.
To say the U.S. automakers had little to offer is unfair. To say the inports sometimes had an edge due to cheap labor would be more like it.
I never heard of a 2.5 4 cyl in a Fairmont. I know they did offer the excellent 2.3 Lima (Pinto) engine in the Fairmont, usually in a fleet vehicle with a 4-speed stick.
The Ford Pinto was replaced by the 1981 Escort. They both sold like hotcakes.