You seem to miss the point that the bread of the Passover happened before the advent of either the Law or the prophets. the bread of the Passover was unleavened, because leavening bread takes a lengthy process -- time which the refugees didn't have.
Your exegesis is cute, but mistaken.
You need to heed the testimony of Yeshua, who said, "beware of the leaven of the Pharisees".(Mt 16:6) And the "Word" is the alpha and the omega. It is the beginning and the end. There is no "Passover before the Law and the prophets" for the "Word". The "Word" is from the beginning.
As for you not understanding the concept of using unleavened bread with respect to the last supper, that is as written, and according to Scripture.
Is 8:9-10, " Than I heard the voice of the Lord, saying, "Whom shall I send, and who will go for us?" Then I said, "Here am I. Send me."
And He said, "Go, and tell this people;
'Keep on listening, but do not perceive; Keep on looking, but do not understand.'
The consequences of this can be seen in Rev 18:4