Some of these Old Covenant examples have been adopted into many legal systems
It appears you're attempting to blur the line between law and morality. The Torah is a volume of law, not morality.
Laws deal with what is morally right and wrong. The Law of the Torah deals with what is right and wrong. It is a set of governing principles for people to abide by. There was a reason God prescribed what He did.
As you said, it is the "day-to-day," one day of which was to be treated differently than the others; a day to consider the law of God.
I'm not familiar with that "day to day" statement. Let me expand on what I mean. Where there is a change of covenants there is a change of the law. The NT is a covenant of grace, the OT was a covenant of works. Jesus meets the requirements of the law on behalf of the believer, satisfying the righteousness of God. He meet every jot and title of the OT law. That, in part is why the NT is a better covenant.
God does not neglect the Law. He fulfills it on behalf of His Son. The Person we have wronged with sin is God. He is in a position to forgive, yet He is also a just Judge. That is why the Son becomes a human being, to meet all the righteous requirements of God and restore humanity's relationship to God. A criminal is separated from society because of his/her wrongdoing. In the same way we have been alienated from God because of our wrongdoing and Jesus sets the record straight. Since God is the One offended, He requires justice, either fulfilled in the Son or in ourselves.
The law is specific. Morality varies. Morality is much closer to theistic religion than to law.
The judgments of the law varies depending on the situation but the law is based on particular principles of morality (what is right and wrong). Yes, sometimes laws are unjust.
Murder is wrong, but what defines or constitutes murder? Is self-defence murder? Is a JUST war wrong? No, there is no malicious intent in protecting yourself. Moral aspects of the law vary.
One cannot blend moral and legal.
Are or should laws be based on what is right and wrong? How can the two not be blended?
Actually, one can; it is limited to a judge, who first settles law, and if it has been broken, and then settles punishment for lawbreaking, where the morality of mercy plays a hand.
The law is a set of rules to judge between right and wrong. Mercy is at the discretion of the judge or court, but if someone has broken the law the penalty has not been met until the payment is made. That is why God is mercify as well as just. He meets the penalty in the Son on behalf of those who believe, and gives us His mercy because of the Son's act of grace. Jesus meets the justice of God in paying the penalty. If you are guilty before the law of owing someone more money than you can afford to pay and someone else steps in and pays the penalty then the debt is met. That is the grace and mercy of God. He is the offended party. He is the one wronged. He is the one who accepts the payment of Another on our behalf in meeting His just standards. The penalty is paid for those who rely on it. Others do not accept it and want to pay it themselves. That is their choice.
But mercy does not negate the law; it has been broken, which the judge acknowledges. But the judge is in a position to determine case-by-case disposition, and may find that a severe punishment does not fit the crime and its motivation, and may, therefore, apply mercy. Mere lawyers do not have that flexibility.
Sometimes the judge acts as God in such cases. The difference is that the requirements of the law have not been met if the penalty or time served varies between people. It is not equal justice for the crime. Sometimes built into the law of a country there is a principle or provision such as The First Offenders Act to go easy on a first offence if it is a minor offence. That is where grace or mercy comes in. The situation varies depending of what law is broken. But for someone who commits murder they deserve to go to prison. The time they serve may depend on the circumstances involved, such as first-degree murder, second-degree, and so forth.