There's a lot of truth in what you wrote, but I have to disagree with your conclusion (which seems to be that the OT is useless and there's nothing in it for us).
Please don't misunderstand me, I am not saying that NT gifts and stuff were given to all in the OT or anything like that. I'm saying that there's many prophetic truths in the OT which spoke of and pointed to The gospel of the NT. Types and shadows.
Shadows is a good description. It is the age of the gray. Jesus was the light. Who would return to gray and leave the light?
The same spirit that caused the gray can influence the light if we go backward.
Gnosis tells us that it was Christ who caused Adam and Eve to eat. Was it the Tree of Life, or the Tree of Death? One said man would die. Another said man would gain knowledge. Who is truth?
The spirit was given to man to save him. Christ said it is the spirit that quickens us. Through the ignorance of the OT, came patriarchy, murderer, lies, adultery, jealousy, etc. Did this come from the soul or the spirit?
When Christ said that Moses didn't get his spiritual food from heaven, what are we to think? When he said that he was "from" heaven, who should we believe?
If the OT teaches anything, it reveals both influences. The life giver and the murderer. We know the murderer existed in the OT because Christ says so.
The only profit of the OT is to prove that Jesus kept the promise of "certain" truths the Jews were told. And through spiritual knowledge, we see the difference between the ignorance and the knowledge (spiritual).
Christ said teach the Gospel. That is not the OT. The church fathers taught it and became murderers as the Jews did. This is NOT Christs teaching (Gospel) and if one is not careful, the "liar and murderer" will corrupt the very Gospel Christ taught.
I don't need the OT. I am a Gentile as those Paul taught. And not influenced by the false gospel Paul spoke against in Galatians. 6 chapters worth reading that shows the emerging ideology of the Pharisee's that tried to use the Law to dispute spiritual truth from Christ, and that the early catholic ideology was dragged into.
Galatians 1:
6 I marvel that ye are so soon removed from him that called you into the grace of Christ unto another gospel:
7 Which is not another; but there be some that trouble you, and
would pervert the gospel of Christ.
8 But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed.
9 As we said before, so say I now again, if any man preach any other gospel unto you than that ye have received, let him be accursed.
Paul mentions the Incident at Antioch, in which the Jews tried to incorporate their OT beliefs into the definition of Christianity. And accused Peter of bowing to such ignorance.
Galatians 2:
11 But when Peter was come to Antioch, I withstood him to the face, because he was to be blamed.
12 For before that certain came from James, he did eat with the Gentiles: but when they were come, he withdrew and separated himself, fearing them which were of the circumcision.
13 And the other Jews dissembled likewise with him; insomuch that Barnabas also was carried away with their dissimulation.
14 But when I saw that they walked not uprightly according to the truth of the gospel, I said unto Peter before them all,
If thou, being a Jew, livest after the manner of Gentiles, and not as do the Jews, why compellest thou the Gentiles to live as do the Jews?
15 We who are Jews by nature, and not sinners of the Gentiles,
16 Knowing that a
man is not justified by the works of the law, but by the faith of Jesus Christ, even we have believed in Jesus Christ, that we might be justified by the faith of Christ, and not by the works of the law: for by the works of the law shall no flesh be justified.
Paul continues in Galatians to refute the gospel the Jews proposed. Basically, including any part of the OT that was Judaism. Read Galatians with a spiritual open mind, and it reveals what was emerging, and how Paul tried to prevent it.
The church fathers wound up accepting the "other gospel", that redeclared the priesthood, something not found in the Gospels or Pauls 10 letters.