Legacy costs aren't going to go away unless they declare bankruptcy or the USA implements single-payer, federally funded healthcare, so their labor costs will be higher than say, Toyota or Hyundai. That being said, Mercedes and BMW in Europe don't exactly have low labor costs either, so one possible decision is to follow the Germans and move upmarket in search of higher profit margins, leaving the bottom end to the Japanese and (later) Koreans. Unfortunately GM management took the opposite direction and cut costs relentlessly, and since labor costs were hard to cut, it was the materials, workmanship, reliability and engineering that suffered, and their market share suffered along with it. A Cadillac DeVille from 1967 feels far more upmarket than its 1987 counterpart filled with chintzy plastic and fakewood. IMHO Toyota in the mid-2000s were heading the same way, with an entire decade of declining materials and build quality behind them, but management was apparently smarter than 1970s GM, and they've fixed the problems since.
Earlier embrace of fuel-efficiency technologies like fuel injection and 4+ speed automatic transmissions wouldn't have hurt either.