I bolton, I’ll carry your take forward as I reflect on the script. I haven’t seen the movie. I have a screener and my oldest son has recommended it highly. The script reads like a slow descent into madness, but your structural analysis may well fit.

One thing I was surprised to see in the script: the prevalence of sexuality. Masturbation. Humping mattresses. Fantasies about mermaids. Homoeroticism. If I were Freud, I’d probably zero in on the lighthouse itself as a phallic symbol.

Have to do much more thinking about this and the story overall to see where I land in my understanding of it.

By way of background, here is an interview with co-writer / director Robert Eggers.