Blame the Self-Seen Victim
To a large extent, your happiness results from your comparing your situation to your expectations for that situation. You are happier the better you are, compared to what you would have expected to be.
Both of these parameters vary with how you frame their context. Especially your expectations. Do you compare yourself to your most successful siblings or childhood friends, or to the average human, or animal, in history? We all know that we have choices about how we frame such things, and thus we know that we would be happier if we were to choose framings that lowered our expectations.
But we mostly refuse to so choose. Plausibly as a negotiating tactic. Others may on average treat us better if they fear being censured due to the combo of their doing blamable things and us acting like we feel mistreated. Whereas if we always act happy and content, they may think they have much less to fear from anyone complaining that they have mistreated us. So in this way being unhappy is somewhat adaptive.
Of course this tactic makes less sense early in life before others have had much chance to mistreat you, and before others decide whether to associate with you at all. But once you’ve accumulated associates who might plausibly be blamed for your situation, and who can’t easily break away from you, the tactic makes more sense.
None of which is to say that people aren’t sometimes mistreated, nor that fear of being blamed for mistreatment doesn’t cause less of it, which is good. But this does clearly imply that people are to a large extent to blame for their unhappiness. Including many who really are victims. Yes, blame those who see themselves as victims for much of their unhappiness.
Agree that people acting aggrieved are often selfish in doing so. People instinctively distance themselves from community members making such shows - the winning move is not to engage.
If I understand the novel angle here, it's that necessarily some of the unhappiness is chosen by the biggest complainers (it's traded away to generate more accommodations from people who are stuck with you). This seems to assume a kind of standard not-explicitly-deceptive authentic emotional human who has to work themselves up into real misery in order to credibly signal it. I think we don't quite have this when 1. cultural resources arise transmitting learnable tips for gleefully scamming w/o unhappiness 2. constitutionally different outsiders with a different victim-happiness tradeoff enter a population that doesn't yet recognize this fact (in both cases i'm positing advantages in successfully imposing a felt obligation in the community for how much unhappiness is felt by the complainer)
I'm going to keep on blaming the perpetrator.
We evolved instincts to empathize with those who suffer, for a reason. Throwing these instincts away sounds like a genuine example of the "drift" you talk about.
To a large extent it doesn't matter what emotional signs the victim is giving off. You ask yourself: did the perpetrator do what they are accused of? Did the perpetrator lie about it? Did they treat the victim disrespectfully? Did they act in accordance with the golden rule? Did they abuse their power? That's all you need to know about the situation.
Abuses of power are a much greater danger to society than the occasional exaggeration of emotional impact from a victim.