The 70s were an absolutely dismal time for American car manufacturers. Seriously, they were, with few exceptions, fucking terrible from about 1973-84.
It's called the malaise era specifically because of a Jimmy Carter speech from 1979 during the second energy crisis of the 70s.
Because of the hubris of American carmakers, the increasingly stringent emissions controls led to such travesties as the Chrysler LeBaron with the "Lean-Burn" 318(5.2L V8) that made less power than a contemporary Datsun 810 with a 2.4 inline six. These cars cost about the same.
Seriously - this car had a 5.2 liter V8 that made all of 120 hp, was generally on the bad side of 17 mpg, and was built on the same frame and platform as a 66 Dart.
Meanwhile, this slightly smaller but still roomy Datsun was within $250 of the price, was faster (due to weighing 600 lbs less and having a 5 hp advantage over the LeBaron,) and more reliable, and used only about 2/3 the fuel that the Chrysler did.
The 70s weren't all a wash, though. GM F-bodies of the time were some of the best-handling cars on the road - specifically the 77-81 Firebirds with the WS6 package. The Cadillac Seville from 1977 was their first foray into a new, younger market segment and it worked out well, until they fucked it up in '81 with the BustleBack, Olds Diesel, and 8-6-4. As Mike Spinelli describes it:
V8-6-4 refers to an early cylinder-deactivation feature so ahead of the curve, it never actually worked,
Like all Pandora's Box situations, however, there was hope. GM redesigned their B Body cars for 1977 with a bigger focus on quality and they became some of the best selling cars in the US. Ford introduced the Fox and Panther platforms just before the end of the decade and kept them around for over two decades. Ford and Chrysler both dipped into their European divisions to introduce some of their most successful small cars — vehicles that helped keep them afloat.
But by and large, 70s American cars were shit.