I don't think people who are poly should automatically assume that the desire of one partner always outweighs the other.
I think this is such a nuanced topic though. It depends exactly what you mean. What most people entering ENM mean when they say this is that they're not going to sacrifice what they have for anything new. Sometimes they're naive about that, admittedly.
They mean the desires that impede on the stability and/or progression of their current relationship are secondary to those of their current partner. They mean the desires that directly involve the hinge. They don't mean all desires are less important and the world should view the new partner as less important than the wife. They just mean that they're more influenced by the desires of their spouse should there be a clash of needs.
My problem is that there seems to be a sense of entitlement from this Reddit community and others who share this view. It's like, they think people aren't allowed to feel that the desires of one partner are more important than those of potential or other current partners. It's like they want to control their potential market so they won't run into this problem where some dude thinks his wife is more important than they are. And I say that because it is mostly women Over there (and forums generally).
A few of them (IMO) use masculine names and pictures to try and give their statements a neutrality which i find very interesting. They're aware that there's something gendered about this and want to disguise it because they don't want it to be about their own socialization. This is just my speculation btw.
It's also as if the Hinge's own desires are secondary to both spouse's and the new partner's, too. It doesn't occur to them the new person that the spouse might be offering a lifestyle and relationship that is aligned with more long term goals and therefore, sustaining that relationship is more conducive to their overall happiness. All they can think is what they're owed by someone's else's spouse.
It makes me rate prescriptive hierarchy, in truth.
It's far more complicated than 'it's good or it's bad'.
What they say they want is for everyone who is a nesting relationship, a co-parent or a spouse to admit that they have a hierarchial relationship. That way, they can know you're worthy of not just rejection, but unsolicited critique.
It's a control technique - if I can convince you that you are a bad person by using the right type of stigmatising language, then you'll feel compelled to gain my validation by changing. Either that, or you'll become very defensive or even hostile towards me for making such accusations just because I do things in a way that doesn't suit you.
PS: link the thread when its created. It will be like when "the pod" descended on us.