Your argument is based on false information and assumptions.
"Assume on the very first day when Gabriel speaks to prophet Muhammad tells him that Jesus is not the Son of God; he is a prophet sent by Allah who is the God."
Why assume? We know what Angel Gabriel said to Prophet Muhammad (saw).
The first time Angel Gabriel spoke to Prophet Muhammad (saw) he never mentioned anything about Jesus.
Prophet Muhammad (saw) had the habit of meditating in a cave in Mount Hira (near Mecca), Gabriel suddenly appeared to him and said, “Read!”
Prophet Muhammad (p.b.u.h) at first thought that he was expected to read actual script, which, being illiterate, he was unable to do, so he answered, “I cannot read”. But the angel said a second time,
“Read!”; and again Prophet Muhammad (p.b.u.h) replied, “I cannot read”.
At this Gabriel (paraphrasing the Prophet)“…seized and pressed me to himself until all strength went out of me. ‘Read!’ the awesome voice commanded again; then he released me…” and Prophet Muhammad (p.b.u.h) then received the first lines of the Qur’an.
Recite in the name of thy lord who created,
Created man from a clot;
Recite in the name of thy lord,
Who taught by the pen,
Taught man what he knew not.
Nothing about Jesus or son of God here.
Since prophet Muhammad has no clue who this intelligence is, he goes to a Christian leader to clarify this matter (God spoke to them first and they are the best people to know about their God than anyone else).
He did not go to any Christian leader, he went to his wife Khadija.
And she went to her cousin who was a Christian scholar not a leader his name was Waraqah ibn Nawfal.
He practiced the pure form of monotheism in the pre-Islamic era and
used to write Hebrew letters. He would write from the Gospel in Hebrew, and hence he was well versed in Gospels.
This very fact tells us that Prophet Muhammad (saw) was of rational mind and so he sought confirmation for his experience.
which Waraqah ibn Nawfal confirmed that indeed it was Angel Gabriel, same angel whom Allah sent to the Prophet Moses (pbuh).
Waraqah said, 'That is the same angel whom Allah sent to the Prophet Moses. Should I live till you receive the Divine Message, I will support you strongly.'" (Bukhari 4:55:605.)
So here what kind of response we can expect from the Christian leader? Will that leader tell prophet Muhammad that the claim made by the intelligence is true? Obviously, you would know that the reply would never be a positive one.
There is no response from any Christian leader and none expected because prophet Muhammad (saw) did not seek any confirmation from them nor consulted them.
Hardly any body knew about this incident at that time except few including his wife and her cousin.
Regardless of the reply, assume further that prophet Muhammad ends up in contacting so many Christian leaders as well to get a better understanding of this controversy. What will their reaction would be?
What controversy? There was none,
Why you keep assuming? put forward some evidence instead.
And he did not contact any Christian leaders.
You are making false assumptions without evidence.
I like to know, based on what reasoning prophet Muhammad came to the conclusion that Allah is the God and Jesus is just a prophet sent by Allah? is it because of the claim made by the intelligence itself? If an intelligence told this to prophet Muhammad, does that mean that the intelligence lied to prophet Muhammad (by telling Jesus is a prophet and Allah is the God)?
The personal contact with Angle Gabriel and the fact that a Christian scholar confirming it that indeed it was the same same angel whom Allah sent to the Prophet Moses hence he needed no further confirmation.
In fact later on Jewish scholar of Torah by the name of Al-Hosayn ibn Salam whom People considered him a rabbi and who later converted to Islam.
confirmed the claim of Prophet Muhammad (saw).
"The Prophet agreed and invited prominent Jews to visit him.
Then he asked them, “What is the status of Al-Hosayn ibn Salam among you?” They replied, “He is our leader and our rabbi.”
The Prophet (peace be upon him) asked, “If you come to know that he has accepted Islam, would you accept Islam also?” They said unanimously, “God forbid! He would not accept Islam. May God protect him from accepting Islam.”
At this point, Abdullah (Al-Hosayn) ibn Salam came out from the room and announced: “O, The assembly of Jews! Be conscious of God and accept what Muhammad has brought. By God, you certainly know that he is the Messenger of God and you can find prophecies about him and mention of his name and characteristics in your Torah. I for my part declare that he is the true Messenger of God...”"
This conflict of beliefs/claims, is a huge problem in Abrahamic religions.
No such problem exist rather there is difference and commonality among Abrahamic religions, With Islam being the most strict and pure monotheist religion amongst the three.
Also, imagine the situation if I tell Muslim people and Christian people today that Leonardo is the God. Further, that Allah is not the God and Jesus is not the Son of God either. What will they think of me?)
If you make such claim I will ask for evidence.
"Burden of proof lies with the one who makes the claim."
Now I make a claim that Only God as described in the Noble Quran is the true God i.e. Allah.
Here is my proof...
"Rational, logical argument with scientific evidence for existence of Allah"
https://www.quora.com/What-makes-Isl...er/Ajazz-Shake
In prophet Muhammad's case, how did prophet Muhammad come to the conclusion that Allah is the God and Jesus is not the Son of God? And how he came to know that the intelligence was not lying?
Already answered above
The fact that whole of Araba converted to Islam means Prophet Muhammad (saw) proved to the people that indeed he was a true prophet.
Therefore, because of this issue, either we have to say that someone deceived prophet Muhammad or if not we can say that someone has deceived Christian leaders. One of these assumptions has to be true.
Don't depend on assumptions
Here is the evidence for Quran as word of God.
https://www.quora.com/Who-wrote-the-...er/Ajazz-Shake
Here is evidence for Jesus is not son of God.
https://ehrmanblog.org/is-the-trinity-in-the-bible/
https://ehrmanblog.org/tag/son-of-god/
To fix this issue, let's say that someone says that the Christianity was created by Satan and they were deceived Satan.
No Muslims claim such thing,
The true teaching of Jesus (pbuh) were from Allah (swt) later on Christians scholars and church changed and corrupted the teaching of Jesus to suit their own agenda.
But Allah did not say anything to Christian leaders (till the 7th century and even up to this day, he totally neglected the issue) and instead of fixing the issue, he used prophet Muhammad and worked with him for 24 years (had enough time to fix it) to spread the word about the Quran. By doing so, he made the situation worst since now Christians and Muslim people have a reason to argue and kill each other as well based on religious beliefs. Therefore, if we take this hypothesis to fix the issue, this hypothesis tells us that Allah has no knowledge or an intelligence to resolve human issues, other than creating more and more conflicts or if not, this whole story implies that an intelligence was deceiving prophet Muhammad. How can we explain these controversies? If so, based on what reasoning?
This is Slippery Slope argument!
You are making false conclusions because of your lack of understanding of Islam and its teachings.
If Allah wanted he would have made everybody Muslims.
"If it had been thy Lord's will, they would all have believed ,- all who are on earth! wilt thou then compel mankind, against their will, to believe!” [Noble Quran -10:99]
So if Allah wants he can fix all the issues that exist on this earth.
But our life on this earth is meant to be with issues so that we can make choices.
Because our life on this earth is test and we go through this test by using our free will.
“Verily, We shall test you with some fear, and hunger, and with some loss of wealth, lives, and offspring. So give good news to those who are patient. Those who say, when inflicted by hardship, ‘Verily to Allah we belong, and verily to Him shall we return,’ Upon them is the blessings of Allah and His mercy. And they are the rightly guided.”(Surah Al-Quran 2:155-157)
I think you need to study Islam properly but you must set aside your confirmation bias.
Here is something to expand your perspective.
For what purpose would Allah have created us?
https://www.quora.com/For-what-purpo...er/Ajazz-Shake
Why are there so many religions?
https://www.quora.com/Why-are-there-...er/Ajazz-Shake
And Allah knows best.
Have a nice day.
.