While a good deal of what you say in the OP has merit, I would question your contention here.
'Freedom of belief' was not anywhere endorsed in the ancient world of antiquity from which the Qur'an emerged, so I would find it odd to expect it to teach such a radical doctrine.
The Greeks did not tolerate Socrates preaching about an inner deity of 'conscience' to which he had access outside the Athenian gods of the city, so they executed him and persecuted his followers.
The Romans were more 'tolerant' of cultic diversity but didn't believe in freedom of religion: you could keep your native gods, but you had to honour the state religion of the emperor as a living deity and recognise the gods of Rome with sacrifices on top of or subsumed within your native pantheon, or else you'd be variously penalized, depending on the generosity of a given emperor or procurators. Thus we find that worshippers of Magna Mater, the Asiatic Mysteries, Mithraists, Jews and Christians were variously persecuted, executed or simply discriminated against under the Republic and Empire. Freedom of religion,
per se, didn't become a legal norm until Constantine passed the Edict of Milan in 313 (that proclaimed to all "
religions the right of open and free observance of their worship for the sake of the peace of our times, that each one may have the free opportunity to worship as he pleases" for the first and last time in Roman or Byzantine history), and which stayed in place until Emperors Gratian, Valentinian and Theodosius revoked it in 380 by making Catholic Christianity the new state religion in their
Edict of Thessalonica.
Theodosius followed this with the prohibition of all pagan sacrifices; and when he was established as sole Emperor (following Gratian's murder by his own troops) a series of edicts were issued in 391 AD - 392 AD abolishing pagan cults and ceremonies, although paganism as such didn't vanish entirely until the sixth century in Byzantium.
Among the early church fathers of Christianity, such as Lactantius and Tertullian, a belief that religion was above all a free choice in accordance with one's conscience first emerges (and was implemented, for nearly 70 years, by the first Christian emperor Constantine in 313), but while it was still paid lip-service to in principle in the Latin West (not the orthodox east), later church leadership departed from it as the state in the West began to prosecute and execute both apostates and heretics with clerical connivance.
Against this background, the Qur'anic teaching doesn't seem at all reactionary: it was actually fairly enlightened - and I say that as someone who is not well-disposed towards other elements of Qur'anic ethical norms. By the time Islam came on the scene in the 7th century, the world of late antiquity was a bleakly intolerant place, from Sassanid Iran (where Zoroastrians were savagely suppressing Syriac Christianity), to the anti-Judaic legislation of certain Byzantine emperors and their corresponding suppression of the lingering traces of paganism, a trend which perhaps reached its apogee in the Western Holy Roman Emperor Charlemagne's decision, in 722 A.D. during the
Saxon Wars, to order the massacre of 4,500
Saxon pagans and forcibly convert the rest of the Saxon people to Christianity.
We see, for instance, Muhammad stating in the 109th Sura:
Say: O disbelievers!
I worship not that which ye worship;
Nor worship ye that which I worship.
And I shall not worship that which ye worship.
Nor will ye worship that which I worship.
Unto you your religion, and unto me my religion.
While this was a Makkan sura delivered
before Muhammad became a military leader who fought idolaters and smashed their statues (according to the traditional Sunnah accounts), verse (
ayah)
256 of Al-Baqara which includes the aphorism, "
there is no compulsion in religion, the right path has been distinguished from error" is, to my understanding, widely recognised as Medinan in origin.
How one reconciles this with later Hadith, which interpret the infamous and equally Medinan sword verse of the Qur'an (
"slay the polytheists wherever you find them") as mandating the slaughter of infidels if they refuse to either convert or pay the poll tax (there are some hadiths which say polytheists can pay the poll tax like Abrahamic people of the book and some which say they must convert or die), is a question better answered by an Islamic theologian.