Let's see . . . they all have bodies by Fisher, so body quality should be the same. Somewhere in the 40s or even 30s some genius pointed out that all the body envelopes could be the same and differneces between brands could be brought about by fenders, bumpers, trim, badging, and names. Buick maintained a more distinct separate personality with their engines (the only OHV straight 8, and then the nailhead); the dynaflow transmission (villian or hero, it was funamentally different to drive); the most outstanding example of marketing cynicism, the "cruseliner ventiports"--but all in all, there has for decades been darn little fundamental difference between GM lines than styling and badge engineering--especially since the bean counters decreed that the cheaper Chevrolet 350 engine would be used in the Oldsmobile (and other?) lines.
There's not a damn thing we can do to change the velocity of General Motors. We'd be like Mighty Mouse trying to deflect a huge meteor heading for Earth.
Too bad the marketing geniuses don't have the bravery (or brains) to quit trying to produce a separete type of car for every type of person, and go back to the slightly-overlapping heirarchy they had in the 40s, 50s, and 60s. Fewer models, more quality, and some genuine distinction between an Chevrolet Impalla and a Cadillac Coupe DeVille . . .
Get used to the future. It's inevitable.