I'm honestly kind of surprised they haven't tried hiring different actors for the superhero and the alter ego. It would be especially easy with someone like Spider-Man, or even Batman. For SM his face is completely covered in the suit, so all you'd need to do is dub in the dialouge from the actor playing Peter Parker. Same goes for Batman, although for him you might need a little bit of makeup on the lower half of the suit actor's face if it isn't passably similar to the actor playing Bruce's.They should have hired Brolin to play Batman and Affleck to play Wayne.
That's already happening. It's called using stunt doubles for all the costumed action scenes.
But fans have come to expect an actor to play both the hero and the security identity for at least some time. It maintains the illusion somewhat when an actor does both roles.