Would you agree with that?
Even in societies that tolerated the activity to some extent, it was never legally accepted as the equal of marriage.
- - - - -
That is because it wasn’t considered in the same way as we think of it today. It was more of a dominance thing in Ancient culture (esp Greco-Roman), there were rules that determined if you were a ‘giver’ or ‘receiver’, and tolerance depended upon class of the participants and wealth depending upon time and region.
The Roman Emperor scandalized and horrified Roman society by creating statues of his sex slave, Antinous. Neither the Greeks, nor the Romans, nor the Egyptians, etc tolerated polygamy and considered the practice barbaric.
Polygamy was more often practiced in areas such as Africa and Asia where there was no tolerance of homosexuality.