I would argue that Superman was too early to be regarded as a precursor to the modern superhero explosion.
But, be that as it may, Brando was a fairly straightforward character, though in a fantasy film. Hackman, though having won an Academy award by that point, was nevertheless not yet considered A List at that point. He was somewhat indiscriminate about the roles he took at that period.
Nicholson was the only superstar to take on an inherently silly role in a superhero film to that point.