@ReadWithScepticism You ask "Is the Substance trying to say that an older professional woman cheated by sexism has a repressed desire to perform the sickly little-girl-sugar-daddy persona that she birthed? That deep down we are all prepared to sacrifice life as a real woman in order to become the objectification of the male gaze"
I don't personally think this is what The Substance is grappling with. For me, the casting of Demi Moore is instructive (and genius). She used to be at the top of her game and partly that came from being young and (to many people) beautiful. That youthful beauty cannot be sustained. Her career therefore changed as she got older and other more youthful beauties came along to take her place. This is reflected in the cyclical structure of the film. The implication is that Susan too will be replaced by another more youthful version, and on and on.
Demi Moore has obviously had a lot of work done, and works at staying thin, maintaining a specific physical aesthetic, even though Hollywood doesn't value that in older women.
For me, the film isn't saying that "we are all prepared to sacrifice life as real woman" etc but that institutions like Hollywood discard us and that we are victims of the male gaze. This is represented as a grotesque extreme in this movie because that is in keeping with the genre, but nevertheless it touches on a general truth of female subjectivity. It is certainly true of my experience as an older woman. At the point that you have accrued the wisdom of experience you become redundant (it's true for men too, but may play out in a different way). I even identify with the fierce cruelty of some younger women towards older women. I don't know if they intend it, but there is sometimes a gleeful recognition that the world belongs to them now and that the older woman should jog on.
Oh, and the emptiness and isolation the film captured was great because it suggested to me that behind the illusion of glitz and glamour of Hollywood is a more depressing reality of loneliness, isolation and self doubt. She has no friends because if people got to know the real her it would blow the glamour because she is after all just another person (this isn't explicit in the film but is based on the couple of "stars" of my acquaintance. Most of us know of at least one don't we because these people went to school with us or grew up in our neighbourhoods. They are real people).
I am very much enjoying this conversation, by the way. My old brain cells are sparking into life.