You obviously have difficulty with reading comprehension. You should recall I said that God approved of polygamy "...at various times..." While there may have been cultural polygamy during NT times, it was not generally recognized as one of the "various" times God required or approved of it.
It would appear you acknowledge "various" OT patriarchs practiced polygamy with God's approval, and sometimes with his disapproval. David's plural wives were only a problem with God after the Bathsheba incident. Although Solomon had problems later in his life God allowed him to build the temple--so he wasn't a total reprobate with several wives until later. I never claimed Noah and his sons had multiple wives--are you trying to build a strawman?
I acknowledge polygamy occurred in the OT but God never instructed it.
Deuteronomy 17:17 17 He shall not have many wives, that may allure his mind, nor immense sums of silver and gold.
Both David and Solomon were great men but sinners. David inherited his enemies wives as part of his enemies' property, as was the custom at that time. Unless you can provide a Scripture otherwise, his prior polygamy was his own choosing not God's instruction.
Second, Solomon's multiple wives were his undoing and led him away from God as predicted above in Deuteronomy.