That's an interesting point. In orderly, stable concubinage at least the royal mistresses and bastards, bless them, were provided for. I think of the out-of-wedlock Don John of Austria, the hero of Lepanto. I also think of Henry VIII's illegitimate son, Henry FitzRoy, who was made Duke of Richmond and who (if he had lived) would have been allowed to become king under the English Parliament's Succession Act.
I can't approve concubinage, but at least it wasn't straight out perverted. And it was better than Henry's later policy of beheading one wife so he could ("legitimately") marry the next one.