This is what the referenced article was addressing among other things - that a great lot of people have been "reduced" to listen and decide what great classical music is, according to how much 'film-music' value that music contains, i.e. anything that contains material that's more or less easily classifiable and pigeon-holeable to one or more of mainstream soundtrack categories: action, drama, comedy, horror/suspense, fantasy, western(!), etc., but this is too superficial (or severely limited) when it comes to listening to superlative classical works, and that is where the example of the 'Out of Africa' main title vs. Prokofiev's 3rd Piano Concerto comes in. John Barry's sensuous beautiful moment is something that instantly captivates a contemporary educated urban (not the genre) audience, and some may actually think it is a superior work to Prokofiev's masterpiece, which in all aspects (inspiration, originality, scope, sophistication, melody, harmony, orchestration, polyphony, form, etc.) drowns the otherwise - like you say, fits the film perfectly, stands on its own as music - great soundtrack.
The problem is, that people today may say exactly what you started your post with: "Music, to me, is emotion". It would be more appropriate to say that most - if not all - music provokes an emotional response. The problem is that the increasingly unsophisticated audiences of today fail to understand that although music provokes an emotional response in them, it also carries stimuli that also provoke a lot of mental calculation, scrutiny, and analysis, which are the result of the composer's self-imposed challenges in a work. The harder and more complex the challenges are, the harder it is for the composer to satisfactorily meet those challenges (the determination of which depends on the musical materials exposed), the higher the expectations and "anxiety" (emotions) on the educated audience. As they monitor in real time the composer's journey and the creative tools he uses to respond to these challenges, the audience's emotions fluctuate in general (ups and downs during the work). If the composer is gifted both in the setting of the materials, but especially in the way he deals with those materials and "makes sense of them", i.e. the way he articulates his journey and solutions, and the more satisfying the mental closure, the greater the emotion and fulfilment the audience will feel in return. And all that is on top of a great tune that might be contained in the work; I mean of course it is part of the whole, but most times it won't be the raison d' etre of a work, as many times it is in film-music.
This failure to notice all this on the part of the modern audience, is due to the - correct for its purposes - superficiality of most film-music, which usually requires digestion and enjoyment on one - maybe two levels (as opposed to Prokofiev's masterpiece, which actually yields infinitely greater fruit when one digs a little deeper, for there actually exists depth there to be dug).
Of course composers should only be reviewed according to the genre to which they contribute, but genres themselves can also be weighed against one another. As far as compositional skills are concerned, if you mean technical skills, they can be reviewed regardless of genre (ex. Williams I would venture is more competent in orchestration - regardless of Spencer's and others' services - than Cage and a host of other classical composers. Hans Zippo on the other hand....)
P.S.: What is an audiovisual editor doing in this forum? Do yo also write, or are you scouting for talent? [;)]