Cliff does not need a solo. If he really needed a "moment to shine", then they'd have a damn song that would have stuck with the score all these years. Giving him a song to sing in all that madness and debauchery makes him part of the Berlin scene, and he's not. He's really on the outside looking in.
It's not a bad thing to have Sally as the center of the show, technically it's a half and half between Cliff and Sally, because the source material that provided the basis for Cabaret was the "Sally Bowles" story from the Isherwood book.
I don't WANT to live in what they call "a certain way." In the first place I'd be no good at it and besides that I don't want to be identified with any one class of people. I want to live every whichway, among all kinds---and know them---and understand them---and love them---THAT's what I want! - Philip Barry (Holiday)