(4)The historical context of previous comic books and previous thought about comic book heroes is not of great interest. Others more interested in that topic should comment on that.
Not to distract from Hirogen Alpha
's qood question, I would like to respond to #4.
One example: Superman as a conscious response to Nietzsche's philosophy as refracted through National Socialism, who increasingly turns into a symbol of America itself (and often an instensely liberal America).
On a bigger level, the superhero represents either an evolution of or a return to the heroic model found in mythology. That the superhero resisted the death of the hero longer than several other genres is interesting, too - it's only with Identity Crisis
that the superhero is inextricably affected by society's embrace of cultural and ethical relativism. Watchmen
is widely seen as the start of that process (although Squadron Supreme
by Gruenwald can't be dismissed).