I can't speak for Marc (and wouldn't presume to), but realistically, his
assessment is pretty accurate.  In fact, the band relies HEAVILY on the very
image that Marc mentions.  It is widely said in the annals of rock music
that AC/DC are very good at what they do, what they do being to play the
same three chords in every single song they make.  And to the
experienced/discriminating rock fan, it's absolutely true.  A great deal of
their music sounds eerily alike.  But that's also what makes it good, and
sets it apart.  They've taken those same three chords, and the
similar-sounding music that results, and developed it into not just an art
form but a science.  Again, I can't speak for Marc, but when I say that
AC/DC is good at what they do (bearing in mind the above explanation of
that), I mean it as sincere admiration.