This kind of reasoning is below threshold.
The virgin birth of the Messiah happened as it was prophesied, why was it necessary? You seem to say prophesy is nothing but it is everything to a believer. Prophesy is the sign to the believer that God is true and is the sign that God uses to set Himself apart from any other god.
Isa 43:
8Lead out those who have eyes but are blind,
who have ears but are deaf.
9All the nations gather together
and the peoples assemble.
Which of their gods foretold this
and proclaimed to us the former things?
Let them bring in their witnesses to prove they were right,
so that others may hear and say, “It is true.”
10“You are my witnesses,” declares the Lord,
“and my servant whom I have chosen,
so that you may know and believe me
and understand that I am he.
Before me no god was formed,
nor will there be one after me.
11I, even I, am the Lord,
and apart from me there is no savior.
12I have revealed and saved and proclaimed—
I, and not some foreign god among you.
You are my witnesses,” declares the Lord, “that I am God.
13Yes, and from ancient days I am he.
No one can deliver out of my hand.
When I act, who can reverse it?”
In case you still don't understand what God is saying- He says this is the way He sets Himself apart; He reveals something before it happens , He makes it happen, then He comes to remind you of what He said earlier when it materializes.
That is why the disciples and even Jesus used to say "this is to fulfill ..." because they understand. And this is how God operates even our salvation is promised- so all our hope is based on prophesy. All the disciples had to do was based on prophesy. Even your denial is fulfillment of prophesy.