'The Beast Below' posits a similar idea to 'The Ones Who Walk Away from Omelas'. In being adapted for Doctor Who the story was adjusted in a few ways I find fascinating.
In 'Omelas', the journey from disgust to acceptance is described as a conscious and active one. It's a journey granted whatever time it needs, of explanation and rationalisation, of decisions made in the safety of alleged objectivity and perfect information. 'The Beast Below' instead allows and requires people to avoid that task completely, by completing forgetting all of it. My experience of difficult moral decisions feels more represented by the latter case — I 'forget', be it by not thinking about a problem, or deciding against researching a topic, or being distracted, wilfully or otherwise, by something else. For some things I might craft some nonsense rationalisation from the facts available, but just as often I'll rationalise in lieu of finding any facts.
Those who leave Omelas are described in a way that feels noticeably more... spiritual. They have as much as if not more conviction and confidence than those who accept, but no time is spent explaining or developing this as the narrator suddenly flips and declares ignorance. To me, it reads as if these people find some kind of 'faith' or other/higher power, and it leaves them incompatible with the explanations of Omelas and ultimately Omelas itself. This is presented with some kind of cautious optimism within the story. In 'The Beast Below', those that protest are killed. Moral victory, if that's what that was, is definitely not material victory here.
'Omelas', in my interpretation, is inviting the reader to question the reliability of the narrator. A lot of words are spent implying some causal relation between the suffering below and the joy above, but none is ever satisfactorily drawn, and any curiosity is squashed with the clear message that ending the suffering would achieve nothing, even for the sufferer. This, however, is no allegory for a real situation. That causal link would never exist. 'The Beast Below' brings this rejection of the premiss into text, as the causal link is explicitly refuted and the suffering ends with no loss of joy. It takes the extra step of stating that the ending of suffering increased the joy, even before considering that the joyful are no longer burdened with a moral challenge.
I could perhaps argue that "the ones who walk away from Omelas" are walking away from the diegesis of 'Omelas' rather than the place: the 'other power' they find is rejection of the story itself. Such people would have no explanations to give for their departures and no possibility of return, and would be beyond the comprehension of the narrator. The challenge for the reader isn't to evaluate their approach to the moral conundrum, but to join them by rejecting the idea that such conundrums are valid in the first place. This might sound like a desire to worm out of a hypothetical, but I consider it legitimate because the whole point of a hypothetical is to help identify a truth, and I just don't know of any truth that we can learn from this hypothetical. I'm very used to seeing real world scenarios get boiled down to some trade-off between some person's suffering for another's benefit, but I don't believe any of these actually hold. Joy does not demand suffering. It can result from suffering, but it doesn't demand suffering. We can eat the good food without a meat industry. We can have services without underpaying service workers. We can have security without inhumane incarceration. 'Omelas' hints at that, but 'The Beast Below', in its own clunky way, focusses on that. 'Omelas' isn't morally wrong — it's just wrong. Why use morality as a weapon when reality will do?