You just have to look at western sensibilities to understand the missing harem trope. The heroes in Western stories have a once in a lifetime romance. If there's a problem with the romance, it's part of the evil plot device (Ursula in the little mermaid.)

Western power fantasy tropes come in the form of the white savior or agents above the law tropes. John Carter was written in the early 1900's, Stranger in a Strange Land by Heinlein in the 60's.

Octavia Butler takes those classically white and Western tropes and turns them on their head.

Also, collapse of society movies are close to American/English isekai because of our obsession with both apocalypse and saviors. Walking dead is a great example.