Respectfully disagree with your theories. The New International Version and the New Living Translation both call those virgins "bridesmaids," not brides. And most plural wives were added one at a time, not in groups of 10 or more. Men's ability to perform hasn't changed that much since the old days, even the young ones.
Jesus' saying that he came not to replace the law but to fulfill it had to do with the promises of God to his people in Isaiah and elsewhere that a Messiah would come. Your theory is contradicted by most of the epistles, which explain over and over that legalism in following dietary and ritual laws is not the path to salvation, and that following Christ's teachings from the heart frees both the circumcized (Jews) and the uncircumcized (Gentiles) who follow him from the obligation to observe ritual minutiae.
And lastly, while King David's six wives may have been counted a blessing, they, too, were before Jesus' time. Jesus spoke of one husband and one wife. He overturned more than the tables of the tax collectors.