it's also possible to have healthy, non-hierarchical poly relationships. many queer people do it with triads, quads, etc. most of the hetero poly people I met and were icked out by functioned as extremely hierarchical in practice (but they would love to tell you about how they were relationship anarachists or whatever) with a couple at the center and one of the partners being the one that pursued having a lot of other partners while there was hidden pressure for the other to also engage in the practice so they didn't seem patriarchal or toxic (a cruel irony, in retrospect)

that said, my observations have a sample size of like... four couples maybe? (they're indistinguishable from one another now). but the dynamics I saw were four for four which seemed good enough for me at the time to dip out of that scene

One might also argue this is more mainstream in some cultures, and it's just not talked about. In countries such as Japan or France it's not uncommon to have a mistress (or male equivalent) but also having a primary family. That's hierarchical polyamory with uh, less steps.