“For if that first covenant had been faultless, then no place would have been sought for a second. Because finding fault with them, He says: ‘Behold, the days are coming, says the Lord, when I will make a new covenant with the house of Israel and with the house of Judah—not according to the covenant that I made with their fathers in the day when I took them by the hand to lead them out of the land of Egypt; because they did not continue in My covenant, and I disregarded them, says the Lord...’” (Hebrews 8:7-9).
“If it ain’t broke, don’t fix it” is an axiom God and other wise persons operate by.
IF the covenant made at Mount Sinai—with its succession of High Priests who needed to make daily sacrifices for their own sins—was the best solution to restoring fellowship with humanity, then God would never have sworn to David of a better priest, one after the order of Melchizedek (Psalm 110:4).
IF the covenant mediated by Moses and the angels had brought perfect fellowship between Jehovah and humans, then God would never have prophesied through Jeremiah that He was going to make a new covenant which was different and better than the one made at Mount Sinai (Jeremiah 31:31-32).
IF the first covenant had been faultless, then God would never have made and implemented a second and better one.
The fact that God did provide a replacement for the old covenant tells you everything you need to know about it and its replacement. God does operate by the wisdom of “If it ain’t broke, don’t fix it.”