Music sweeps you up in to the drama of the action by heightening it and makes it believable and makes you forget it's not real by making it unreal if it has the right intensity and impact. It's visceral and could be 100% of the production at times. It's a tug of war that and a marriage that filters in unreality. It sucks the words into an alternate dimension - a world of thought. It gives shape to ideas. It is a dream world and does as much to define a production as anything else. It is also the rudder that steers the ship clear of the coral reef where it could run aground and get lost, so relying on a strong, good main theme is not an unreasonable expectation. It's a simple baby with the bathwater truth. I.e., it could be slightly all important. If it were me I'd have two composers froma perspective stand point as neither they or you really know what they do and don't do well.