Muhammad’s ancestors were pagans who worshipped many gods.
Hmm, what you say here reminds me of the appraisal of Muhammad's ministry that Cardinal Nicholas of Cusa (1401 – 1464) wrote for Pope Pius II in his 15th century study,
Cribatio Alkorani (Sifting the Qur'an) in three volumes.
At the time, Cardinal Nicholas was the most powerful office-holder in the Roman church after the Pontiff himself and in his role as vicar-general in the Papal States (equivalent to our modern day Prime Minister under a monarch), he was tasked with overseeing the diplomatic relations of the Papacy with the new Ottoman caliphate that had been established in Constantinople after its fall in 1453.
The pope wasn't sure how to respond to the new Islamic regime (he obviously had little knowledge of the 'Arab religion') that had replaced the Eastern Orthodox Byzantine Empire and so tasked Cardinal Cusa with undertaking a comprehensive study of the Qur'an in Latin translation, and then provide His Holiness with the brief so that he could inform himself about Islam in his discussions with the Caliph (as detailed knowledge of Islam was, at this time, lacking in Europe).
In the opening prologue, addressed in the form of a letter "
to Pius II, supreme and most holy pontiff of the Universal Christian Church", Cardinal Cusa wrote the following (
see the underlined in particular):
A SCRUTINY OF THE KORAN
As best I could, I made a careful attempt to understand the book-of-law of the Arabs—[a book] which I obtained at Basel in the trans-lation commissioned for us by Peter, Abbot of Cluny. [I obtained it] together with a debate among those noble Arabs, [wherein] one of them, a follower of Muhammad, attempted to win over another of them. There were also [contained therein] certain other works on the origins of Muhammad, his twelve successors in the king-dom, and on his Doctrinae ad centum questiones. I left the book with Master John of Segovia 4 and journeyed to Constantinople, where among the Minorites who were living at [the Church of ] the Holy Cross, I found the Koran in Arabic [...]
Now, since there can be many ways that seem to be good, there remains doubt about which is the true and perfect way that leads us assuredly unto a knowledge of the Good (a Good which, indeed, we call God) in order that when we discourse about it we may understand one another. To be sure, Moses described a way; but it is not accepted or understood by everyone. Christ illumined and perfected this way, though many remain who are still unbelieving. Muhammad attempted to describe this same way as quite easy, so that it might be accepted by all, even by idolaters.
These are the most renown descriptions of the aforementioned way, although many other [descriptions] have been made by wise men and prophets. But all the aforesaid descriptions hold as their basis the view that that oft-mentioned Good is maximal and, thus, is one; and this One all call God...
But Jesus, the son of the Virgin Mary and the Christ who was fore-told by Moses and the Prophets to be coming, did come and did re-veal most perfectly—according to the testimony even of Muhammad the oft-mentioned way [...]
Moreover, if some-one had asked Muhammad in what form God would have sent to men an envoy who was someone greater than an angel, then Muhammad would certainly have answered [that] if God were to send to men an angel as an envoy, He would indue him with human form.
And [Muhammad] would reply similarly if [God] were to send someone greater than an angel. Now, according to Muhammad [God] sent Christ, whom [Muhammad] declares to be the Word of God and the son of Mary. Therefore, since the Word of God is of the same nature as God, whose Word He is (for all the things of God are God on ac-count of His most simple nature), then when God willed to send a supreme envoy, He sent His Word, than whom no greater envoy can be conceived. And because He sent [Him] to men, He willed for Him to put on a most clean human nature. And [Jesus] did so in the Virgin Mary, as is often found written in the Koran.
Therefore, there will be no difficulty in finding, in the Koran, the truth of the Gospel, although Muhammad himself was very far re-moved from a true understanding of the Gospel. Now, must not fail to mention that the chapters of the collection of the aforesaid book of Arab law do not form a continuous sequence with one another [...]
[Followers of Muhammad] also say that God sent to all nations indigenous messengers and that [through them] He admonished these nations regarding what they had to believe and had to do in order to be numbered, on the day of judgment, among those who are good and in order to attain unto the Paradise full of joy [...]
Moreover, [followers of Muhammad maintain] that [these nations] ought to believe those messengers of God and ought to obey the divine precepts made known by them; and in this [belief and obedience the nations] were not able to be deceived. For with respect to anyone who trusts in God (who is most veracious) by obeying His command: how could he find himself deceived on that day [of judgment]? Accordingly, [followers of Muhammad] conclude that if the variety of laws and of rites is found to be present in the identity- of-faith that is exhorted within the various nations by the messengers of God,13 then indeed this [kind of diversity] cannot at all prevent one who is obedient from obtaining a fitting reward at the hands of the most gracious and most just Judge. Now, [the Koran] enumerates the prophets and the messengers of God who were supposed to be believed: [viz.,] Abraham, Ismael, Isaac, Jacob, Moses, Christ, and numerous others [...]
Unless the Gospel is included in the Koran, one cannot say that the Koran suffices and is the right way; moreover, it is evident that, with-in the Koran, only that which agrees with the Gospel ought to be called the light of truth and of the right way. Furthermore, the author of the Koran did not have any doubts about the Gospel; for he cited passages and contents of the Gospel regarding the fact that some [men] turned away from Christ when He expounded the parables 38 regarding the grain of wheat,39 regarding the man born blind,40 and regarding other matters [...]
Hence, if any beauty or truth or clarity is found in the Koran, it must be a ray of the most lucid Gospel [...] Therefore, in the Koran the splendor of the Gospel shines forth to the wise, i.e., to those who are led by the spirit of Christ [...]
Accordingly, the Koran speaks correctly in ascribing to this Word wisdom and every magisterium.97 Moreover, [the Koran] speaks rightly in affirming [the following: viz.,] that Christ made known to the world that He had come with divine power, in order that, as the Envoy of God, who placed all things in His power, He would be able to do whatever men can ask of God.98 For the miracles that Christ worked made known that in Him was the same power which is in God the Father, who sent Him. And in order that the Koran might better exhibit this revealed [power] to the uneducated, it cites briefly His curing of diseases that are incurable by men and His resuscitating of the dead.99 And it even adds—as if to say that He lacked nothing that we ascribe to God—that by breathing into birds made of clay, He gave them life.
Cardinal Cusa, in other words, reached much the same conclusion as you have above: "
The emphasis [of Muhammad] was on moving from polytheism and idolatry to monotheism and a means of worship acceptable to the God of Abraham".
So, he instructed Pope Pius II to proceed in his discussions with the Caliph on that basis. While he disagreed with a number of elements of the Qur'an, he also noted that, "
any beauty or truth or clarity found in the Koran, must be a ray of the most lucid Gospel" and identified parts where the Qur'an "
speaks correctly".
Even when he was at his most vituperative about Islam as in Book II, Cardinal Cusa always seemed to balance it with a subtle positive i.e. "
Nevertheless, God Almighty willed that amid all these filthy and vain things...there also be inserted [into the Qur'an] things in which the splendor of the Gospel was so contained as hidden that it would manifest itself to the wise if it were sought for with diligent effort".
Cardinal Cusa gets especially close to your evaluation when he writes the following in Book II:
A SCRUTINY OF THE KORAN
The goal and intent of the book of the Koran is not only not to detract from God the Creator or from Christ or from God’s prophets and envoys or from the divine books of the Testament, the Psalter, and the Gospel, but also to give glory to God the Creator, to praise and to bear witness to Christ (the son of the Virgin Mary) above all the prophets, and to confirm and to approve of the Testament and the Gospel. [If so,] then when one reads the Koran with this understanding,47 assuredly some fruit can be elicited [from it]...
If Muhammad had simply preached the Gospel to these Arabs and had not given them their own law, they would not have come to the Christian law, which they rejected for almost six hundred years.
Therefore, he preached to them that they were Ismaelites and had descended from Abraham and that both Jews and Christians praised the man [Abraham] as a prophet and approved of his faith— through which faith he obtained from God the greatest things both here below and in the other world.
And [Muhammad preached that] since this [praising and approving] was done by the Gentiles, who after following Abraham in the rejection of idols favored a certain law (whether the law of Moses or the law of Christ), then a fortiori the Arabs, who were descended from Abraham, ought themselves to do [this. Moreover, Muhammad preached] that God had chosen him as His messenger unto them and that God commanded them to accept the faith and the law of Abraham, a most excellent man, who was a believer and who was neither a Jew nor a Christian, having preceded both the Jews and the Christians. Having rejected idols, Abraham turned toward the Creator of the universe and worshiped and obeyed Him, as did also his descendants Isaac, Jacob, and the twelve tribes of Israel.
In the foregoing way [Muhammad] frequently taught the abandonment of idolatry, which, previously, [the Arabs] were never concerned to abandon as a result of the Gospel. [They were unconcerned] especially because evangelical perfection seemed to them to be onerous and to be such that their parents were afraid to accept it. For their parents had been taught (as even the Koran contains) that those who accept Christianity and do not keep its commandments offend against God more than do all [others] and that they will be tormented very grievously in Hell.
Therefore, Muhammad hid from the Arabs the secrets of the Gospel, believing that in the future [these secrets] could become known by the wise—just as in its beginning period the Gospel, too, remained obscure and unknown to many but was made progressively more evident. And if this [procedure] had not been expedient, then Christ would not have spoken to the people in parables....
The faith of the Gospel was despised everywhere by the idolatrous Orientals. The law of the Arabs came as someone unwilling to consent unto the faith [of the Gospel,] and it led the Arabs unto the worship of one God; nevertheless, the Gospel was secretly approved [by the Koran]"