They are completely different mediums though and if Rob Marshall had just filmed the stage show, we'd have all been whining that he'd done exactly that. He HAD to make changes for many reasons and Class had to go because it was inaccurate to their vision (it's presented as an actual number, not a fantasy inside Roxie's head). Seeing the film should make you want to see it on stage and vice versa.
Nothing precious, plain to see, don't make a fuss over me. Not loud, not soft, but somewhere inbetween. Say sorry, just let it be the word you mean.