I'm sorry but I don't really buy the cynical 21st century issue. The 1970s was just as much a time of darkness and cynicism. The President of the United States was resigning because of proven criminal allegations, the US was just humiliated in a controversial war. The world was in economic stagflation, which economists had no idea how to fix. People had 20% interest rates on their mortgages! It was a dark time with a lot of cynicism and uncertainty and Hollywood's output reflected that with antihero films like Dirty Harry and The French Connection or films deconstructing the American Dream like The Godfather or movies about corruption like Serpico. Nevertheless, the bright and hopeful Donner Superman did gangbusters because people were still looking for something hopeful and escapist because it allowed them to believe in something better.
Superman doesn't really need an update for the 21st century, the core of what he is is appealing to us in dark times, which is why it seems like a lot of critics were hoping for a more archetypal Superman from this.
But even if I am wrong on the above, WB had the perfect playbook for a modern Superman in a graphic novel in Mark Waid's Superman Birthright. It has a likeable, proactive, heroic Clark Kent who is faced with cynicism of the 21st century.