I'm struggling to understand the reasoning behind the Islamic version of Jesus the Messiah. Rational reasoning welcome

Islam like Christianity believes that Jesus is the Messiah yet they do not believe that he is the son of God or that he died as a perfect sacrifice for the sin of man. These things are key to salvation in Christianity for it is written "he who denies the son denies the father". "For God so loved the world he sent his only begotten son to die as an atoning sacrifice for mankind so that all who believe in him will be saved".

Islamists believe he was simply a great prophet of messianic importance who was sent to the Jewish people.

In Christianity we attribute Jesus as a parter to God for he is begotten of God and the bible states the fullness of the deity dwells within him. In Islam you can be forgiven for any sin except the sin of attributing partners to God.

So these 2 religions are fundamentally different as salvation in the one equals damnation in the other.

So let me trace the reasoning behind the Islamic Jesus:
-So why does God send a prophet? To deliver a message that makes a change.
-Has God ever in all scripture failed to have his prophet accomplish their objective? No.
-What according to Islam was Jesus's objective? To correct the wayward Jews from their wicked ways.
-What was the result? 2 Billion people breaking the only unforgivable law in Islam, attributing a partner to God.
By the admission of Islam itself Allah made a huge mistake sending Jesus and this single prophet did catatrophic damage to the salvation of man.

If you try to explain it by saying Christians twisted or misinterpreted his message you still have to admit that God's purpose failed for what God sends a prophet he knows will be misinterpreted?

How can the Islamic Jesus make sense in this way?