I come from a "Movie Musical" background. My sister has been a dance instructor her entire life. We've seen nearly every musical ever made.
Know Russ Tamblyn? If you've ever seen a musical odds are you've seen Russ. I've met him several times. He and my sister worked together a few times, she knew him well.. she might still know him well... not sure. Thru dance my sister has met, and occasionally worked with, many of the background dancers in musicals, both old and new.
Be cautious, what I'm about to say might make you nauseous.

. I think Gene Kelly's "Singing In the Rain" performance one of the greatest scenes in move history. Same for Donald O'Connors performance in the same movie. Several other dancing scenes I consider to be the best ever use of celluloid. Yes, I'm a big musical fan.
I do not think Grease was one of the best... but it was very good, IMHO, and "fun".
See? You never want to get me started on Movie Musicals... love 'em. - JamesJM