Cyrano is a trap for musical theatre folk, a beautiful spider web.
What do these characters have to 'sing' about? Well, nothing. Of all the people onstage Cyrano is the only one who can be expressed with any music whatsoever and that includes underscoring and dance as well as song. Cyrano is the poet. Christian cannot sing. He can't even talk. Roxanne cannot hear the singer of the words she loves. None of the other roles are musical in the slightest.
Just because songs can be written in spots for other characters does not mean the role ought to be musical.
Cyrano is the sole person in Cyrano de Bergerac that 'sings' metaphysically and should sing at all. That's a pretty dull show even with the best singer in the world.
There is the beautiful trap. All that poetry, all the romance, but it comes from one character and the others are tone-deaf.
Other posters have written here what I have said. I am not alone. Cyrano needs to remain Cyrano de Bergerac.
"If my life weren't funny, it would just be true. And that would be unacceptable."
--Carrie Fisher