I agree that music is less significant then design, artwork and coding (and don't shoot me since I am a composer and sound designer myself).

Sound design is very important and good solid audio design is often underestimated.

The problem with music is indeed the ego of the composer. Most composers run from project to project without really building a strong solid relation with a project. This is btw not only caused by composers but also often by devs who realise that they want some music in the game and ask at a very late point a composer to work out a score in a very short time, but this is another issue and slightly off-topic.

I think with coming of adaptive music design we can change a lot and music can become an important and very effective part in game design.
We need to learn to adjust to a project and dig into it and know what we should do and what not. Often music is overdone or does not always represent a the correct feeling. We have to communicate better with the devs I think.