Superheroes Are Not Gods
The title is true. And they are not a substitute for the saints. They are not even psuedo-saints. Even though superheroes have cool super powers, they are still characters who struggle with evil within themselves. Iron Man and Doctor Strange both start out as narcissistic jerks, but over the course of the MCU, they become more selfless. So does Thor. And Loki eventually does, too.
These superheroes aren't perfect. They're flawed, just like the rest of us. So while their powers make them god-like, they are far from gods. And that's part of the reason they're so popular. They work to overcome their vices while saving the universe.