But if it's the expected norm for that genre how can it be "service"? since service is defined as something "extra"?
Because of the downplay also existing too. Though you are right we cannot just look at something and go "Fanservice" without knowing what the norm really is.
Just because something is extremely sexual to us it doesn't nessisarily mean it is extremely sexual within its own sphere or culture.
As well we also have to apply the filter that these are going to be "Idealised" and "Exagerated" characters as well.
You can also see if the sexualisation is part of the character or plot, or if it plays against the character or plot.
Finally we also have to apply what I call "Natural sexualisation" which is the sexualisation that results simply by having an exagerated idealised character.
For example people are quick to write off Superman inspite the fact that he is muscle clad with ever single muscle showing and even having quite the butt. Superman by all means if we looked at it objectively is clearly a "Sexual character" given that he has exagerated sexually attractive features. Yet when we apply the filters we see that he is clearly not. (To anyone who argues... LOOK AT SUPERMAN's BUTT! It tends to be a very exageratedly sexy butt)
Thus through this process we have the ability to have a sexy woman who isn't "Sexual for sex sake" and who isn't "unnessisarily sexualised".
which is really what I am trying to get across... The possibilty for a sexy woman to exist outside of fanservice... and NOT because the artist "Had to make the woman sexy or else people would be mad"