As part of a poly family whose members only occasionally play outside of the family, our situation is not the same as regular swinging couples. But as a woman with an opinion, I will respond to the question, "Are both partners equals?" - NO.
We are not equal because we are not the same, even before our poly family formed. There's a difference between women and men; men generally want more sex even in the rush of a weekday morning. Women have a greater capacity for it, taking three or four in a row, no problem. That's why, until recently, we women shared an outside boyfriend while the men didn't play.
We women have a homosexual side, the men do not. One of the guys likes to take us women "fresh" then not watch in his post- orgasm state, while the other likes to "watch the show" in an excited state and go for sloppy seconds.
Lora and I are the only ones who like a little BDSM. only with one another. A lot of verbal degradation, some slapping and pissing. We'd like the guys to be there as an audience, but they refuse.
Recently, I became attracted to another man, and after meeting her, his wife as well. A little soft stuff with him without her knowledge was as far as I was willing to take it. The others in my family knew, and it became our fantasy. My husband turned the fantasy into reality with them. We all played, but it was very unequal. The other couple played mostly with Red and Lora, with hubby, Clair, and me only occasionally jumping in. It wasn't equal, but fantastic.
So hardly anything is equal among couples because of individual differences and wants. It may appear unfair, but with love and kindness, it's for the best.