Duality in horror, and the ending of Peele's 'US'

Duality (doppelgangers, alter egos) is a common theme in thriller/horror texts and films. This goes as far (or further) back as the Victorian period (Dracula and Van Helsing as mirror images/Jekyll and Hyde), and continues today (The Nun, Valak and Sister Irene as foils to each other/the twins in Malignant).

'US' (2019) deals with doppelgangers – every citizen has one, and these 'Tethered' counterparts live in dire poverty in the tunnels beneath the city. They are 'savage' and 'monstrous', unlike their peers who live among us.
Peele's film has strong themes of class and social inequality.

The ending, however, reveals that the protagonist of the film was never one of 'us', but in fact a tethered doppelganger who had switched places as a child. Unlike the rest of the Tethered, she speaks and moves fluently, behaving 'civilised' as opposed to 'savage'.

There is clear commentary in this twist of how the environment and social upbringing of an individual can create a stark contrast in how their identity, behaviour, and habits are formed: The protagonist turned out so different from the rest of the Tethered, only because of the economic and social support she recieved as she was brought up.

How does this twist impact the themes of duality present in horror and thriller genres? Does it make us reflect differently on the monstrous villains we see in Michael Myers or Dr Hyde? Does it make us reconsider their motivations?
Dr Jekyll and Mr Hyde/The Unborn, for example, are strongly contextualised by economic and political commentary.