I agree with both your and James’s conclusion that polyamory and being queer are often intertwined. However, I do not think they are the same thing and describe two different phenomena. I also agree with the conclusion by James that a person who sometimes has sex with a same sex partner is likely queer, but diverge in my opinion by accepting that it is not necessarily so. In this regard I can understand the position of the polycule you have recently associated with who apparently reject the description of queer in favor of heteroflexible.
My understanding is that the descriptor of being queer was adopted by certain members of the LGBTQ community because they found that labels such as bisexual, gay, straight, and polysexual were too restrictive or fraught with cultural connotations. In this regard, to my mind, it seems to be more associated with the expression of one’s sexual orientation and in synch with their gender identity than a descriptor of what kind of partners or how many one has sex with. On the other hand, people who describe themselves as polyamorous seem to have a committed relationship with either one other partner (which remains stable as third parties come and go), or someone who has polyfidelity with a group that remains stable as third parties come and go, but allows for a certain fluidity in sexual encounters with other members within the group. Viewed this way, being polyamorous in my mind is associated more with the sexual, social dynamics of a group of people (at least 3) and not necessarily determinate of, or connected to, a clear identity with regard to sexual orientation. As only one example, I could envision a married gay couple who are self-described as gay being in a polyamorous relationship where they bring other gay men into it. I can understand how they would all identify as gay and polyamorous, but not necessarily queer.
Bottom line: to my mind being queer is a descriptor of sexuality and sexual identity. Being polyamorous describes the type of social unit within which it is expressed. In this regard I tend to agree with the polycule you have recently become close to. I do not have the same lifestyle experience with a queer polyamorous community that you do. I consider myself demisexual. I find intimacy with one dedicated partner with whom I have a strong emotional connection works for me. Polyamorous relationships make me a little uncomfortable, though I am open to the experience under the right circumstances. About 50 years ago I spent part of one summer with the polyamorous commune at China Grade. My experience was that most of the people there “seemed” heterosexual, and were open to intimate encounters with both members and short time visitors. I say “seemed” because this was a time when being gay was still unacceptable to most of society, so possible gay or bisexual people were likely closeted and careful about their activities. I was comfortable in the environment and felt welcome, but it was obvious that certain individuals had closer relationships than others. I never felt excluded, nor did I observe anyone else being treated that way. I was very young at the time and still discovering myself, so a bit more adventurous and experimental than I am today. That is about the limit of my experience with polyamory. I am the first one to admit I am not anywhere near as familiar with your lifestyle as you are. I do not have the same experience. You asked for comments, so this is my understanding of the dynamics you describe. I am well aware that others may disagree.