He states in his book (in chapter ‘midway’ (or something like that) that the Arab astronomers proposed a heliocentric world.

That should settle the confusion.

Of course Islam is what Muslims do. That’s as true for Islam as for any other religion. There is no other practical way to evaluate the precepts of a religion then by observing it in action, since there is no way to get followers of the religion to agree on its precepts. Ismailis and Salafis aren’t going to agree on much, even if they think they follow the same religion. (Interestingly, there is a fair amount of doctrinal support for this position within Islam itself.) I would be very careful of considering Muslims in the past to be paragons and the Muslims of today to be “in the dark”. From there it is far too easy to become a takfiri. The Muslims of history are worse then you think and the Muslims of today not as bad, simply because of human nature.

As per your forced conversion statement: a large number of Muslim countries are close to or wholly Muslim now that weren’t in the recent past. See, e.g. Pakistan, Bangladesh, and Turkey. It is a historical fact that many (though not all) Muslim countries are hostile to religious minorites, even ones of long standing - like Bahai in Iran or Christians in Egypt. There are essentially no Muslim countries that wholly respect freedom of religion - in most Muslim-dominated countries there are legal barriers to the practice of non-Muslim religions. God help you if you belong to a Muslim sect viewed as heretical by most Muslims, see e..g the Ahmadis in Pakistan and Bangladesh.

Yes, the Crusades were bloody and horrific, but I assure you the Muslim leaders involved were not blameless. The proximate cause for the First Crusade was a call for help from the Byzantine Empire to fend off invading Muslim armies, attempting to conquer regions that had never been Muslim. Another rallying cry was the destruction of the Church of the Holy Sepulchre by the Fatimid Al-Hakim, an event that could be compared to destroying the Dome of the Rock.

It’s a natural reaction to attempt to cut off disreputable or horrific actions from oneself and declare the people involved “not true Muslims”, but it is not going to fly. Aurangzeb, for example, did exhibit many admirable qualities, like humility and charity, while being a bloodthirsty bastard, and people to this day honor him for that. You need to accept the bad with the good: Aurangzeb and Akbar, the Taliban fighters who executes teachers of girls and the teachers who risk their lives to teach Afghani girls, Dawood Ibrahim and Shah Rukh Khan, the janjaweed fighter who burns Darfuri villagers and the Darfuri refugee who flees them. All are Islam.