Mass market pop culture in the past wouldn't place the focus on plot elements like multiple dimensions, alternate timelines, elaborate nostalgic homages to different genres of television, stuff like that. The more high concept sci-fi or fantasy might, but not something as basic as a superhero television show. It goes to show that even mass appeal entertainment are now experimenting with nonlinear storytelling.
Alien, The Matrix, 12 Monkeys, Terminator, Fight Club, The Fifth Element, The Sixth Sense, Back to the Future, eXistenZ, Gattaca, The Arrival, 2001 space Odissey, the Shining, Trainspotting, Ground Hog day, Dune, Dark city, Tron, Demolition man, Total Recall, Robocop, The city of lost children...
Nuanced, scify, full of smart details or mind bending films are not new.
In fact, it's really hard to innovate now, because so much as already being covered.
BtTF was a standalone movie, then a trilogy with only two sequels, not either 1) a multimedia franchise like many of the works I've mentioned or 2) an Inception or Tenet type Nolan blockbuster that requires infographics to tease out the plot.