It seems to me that GM could have looked back into history and figured out that duplicate cars don’t make it. The LaSalle lost out when a smaller Cadillac, the model 61 invaded LaSalle territory. GM was succesful when its cars were different–the Chevrolet was an inline 6 with overhead valves, the Pontiac offered a flathead 6 or a flathead 8, the Oldsmobile offered an overhead valve V-8 while the Buick had an overhead valve inline 8. Even in later years when the GM line went to V-8 engines, the engines were all different. Transmissions differed as well–the hydramatic offered on the Oldsmobile was completely different than the Dynaflow available on the Buick. Even the suspensions were different among the GM cars,
The DeSoto of the Chrysler line died because the Chrysler Newport invaded its territory from above and the Dodge from below. The first Edsel had a senior line that was much like the Mercury and a junior line that was not very different from a Ford. In its last years, the Edsel was a Ford with a different body. Saturn started out as a different car, but quickly turned into another rebadged GM car.