I do not agree with everything you say here....before Adam sinned he knew neither good nor evil and had no need of "the law"......just the command not to eat of the tree....the law was not given unto all....only the Jews.....How can the law be perfect in the sense as we use the word? My bible states it is weak thru the flesh and will pass....the bible states that the LAW CAME THRU MOSES BUT GRACE AND TRUTH THRU JESUS and Hebrews is clear.....the entire covenant has been changed from top to bottom....NO MAN CAN KEEP THE LAW, the law was designed to PROVE GUILT NOT SAVE OR EXONERATE anyone.....it is an INFERIOR SYSTEM and had to be changed (see Hebrews) and understand that Hebrews contrasts the Law and Grace and how GRACE is a BETTER WAY AND SYSTEM!
First of all we have to discuss David and Psalms and realise that this warrior of God said that God’s law is perfect and he loved the law very dearly.
Secondly the law was not only given to the Jews as all of Israel was present. The fact is that there were other nations also present with Israel at Sinai the day God asked them to keep His covenant. They all form part of Israel in the end but if we read scripture we see that Israel was not alone the day God led them out of Egypt.
Now to the verse you quote stating the law is weak. The law in itself is weak, without God it is an empty vessel that cannot do anything for you and me. That is why Jesus was so upset with the Pharisees. They knew the law but were far away from ABBA Father.
The only way I can explain it is if we go back in future to the days of the Wild West in America. Imagine what would have happened if you build a highway with five lanes with horse carts and you told the people the speed limit is 85 mph? They wouldn’t know what you are talking about because they didn’t have motor cars. A speed limit to them would not make sense because the vehicle was not there to perform the function.
If we try to keep God’s law without Him being present, central and in charge we are trying to keep a law about something we don’t understand. Is the law good without God being present? No, and never could be but with God being part of the law it is good and healthy for His children.
The law is not an alternative for salvation but give us insight into God's character.
God bless friend.