I love how discussions of varying viewpoints invariably lead to snooty, snide comments ("Clearly, you've never read the Leroux novel"
.
Equally clear is the fact that those who adapt others' work for different media always, always, take liberty with the source material, including both making additions and taking things away; that's what makes the work their own. I'm guessing the Leroux novel didn't feature the Phantom singing every line of text and/or harmonizing with Raoul, either, but there are changes every piece of art adapted from another has to make. The enormous amount of stage-time devoted to the travails of the various peripheral characters could have been better spent on other things -- including, perhaps, scenes from the novel that must have been omitted from the shown, if inventing new scenes out of whole cloth would have been deemed too radical.
The other problem: much of the lyrics sung in the peripheral-character scenes cannot be heard/understood by the audience, in large part because in several of those scenes, many characters are singing different lyrics at the same time. I was sitting fourth row center the other day, and there is nothing wrong with my hearing, but I could not make out what was being said in those group scenes with all of the characters jabbering away, either because of the operatic lilt in their voice, or because they were all singing at once. I had one of those closed captioning devices that enabled me to read what they were saying, but those were not around when Lloyd Webber wrote this decades ago. To the extent that these scenes are important, interesting, or entertaining, I really don't get why it was written this way.
The music from Phantom is some of the best known in the entire canon of musical theater, but no one goes around humming anything Piangi, Carlotta, Firmin, Giry, etc. sings or says.