As for primary/secondary, I think of them as being useful as descriptive categories. A primary is someone you share your heart, body, and your life with, someone you've made commitments with, a life-partner. A secondary is someone you share your heart and your body with, though maybe not in all the same ways, but is not someone with whom you're actively building a shared life. BP is, in fact, Elemental's primary. The gf is, in fact, his (and her?) secondary.
Generally, people who are managing poly relationships that fall into different categories like that (not necessarily because they've been prescribed into those categories, I'm not much if a fan of that, but because that's just how it is) prioritize their primary relationship(s) (yes, you can have more than one). I consider that to be good and healthy. If my gf was regularly considering my needs before those of her husband... the man with whom she shares a mortgage, a child, and a much longer commitment... I'd be not ok with that. I need to be important to her. But for her life to function, considering the much bigger impact they have on each other, he needs to be important to her more. Maybe that'll change some day. It's already shifted in some ways, after 2+ years of she and I being together. But especially when our relationship was newer, primary/secondary was just right/natural, and it still is.
So, no, not every poly tangle needs hierarchy. But I do think many of them healthily incorporate it, and that that's totally ok.
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.