I don’t think that polygamy was ever considered the ideal according to the Torah. The other wife is called a “Tzarah”; I wouldn’t call that managing very well.
Even Leah Imeinu felt that Rochel Imeinu took her husband from her. Imagine how lesser mortals than the Imahos HaKedoshos felt.
In Shir HaShirim, there is one kallah and one chasson. Our relationship to Hakadosh Baruch Hu is compared to the relationship between a wife and a husband (one of each).