The Qur'an appeals to the intellect and reason of the whole of mankind, inviting them to the way of truth. God does not limit His guidance to any culture, place or time.
But reason also says that, realistically, the
degree of opportunity to be a Muslim is heavily dependent on geography and history. You talk about western converts, but these are the low hanging fruit - people who already understand Abrahamic religion and who have at least some access to information. But that opportunity drops to zero for more distant cultures.
Islam should be in the reach of anyone both now and throughout history - yet the hunter gatherers of the Amazon (who live like we all used to, in countless small bands) still have zero opportunity. There is absolutely no trace of the influence of Islamic ideas outside the places where you might expect to find them for historical reasons. As for these tribes, they have not received any messengers, or if they have there is no trace of their message in any tribe today or at any point in history, so their people still have no opportunity.
This opportunity is not at all equal. It's theoretical. And it's easy to find societies where that opportunity drops all the way to zero. To paraphrase a well known phrase: in many societies, it's easier for a camel to pass through the eye of a needle, than for a person to convert to Islam.
This doesn't make sense because being religious naturally involves doing good deeds. The question is whether good deeds done for the sake of God are more worthy of being accepted by God, than those done for the sake of people or other worldly reason.
Being religious should involve good deeds, but that doesn't mean every follower actually does them in practice. Yet the least virtuous Muslim still potentially gets rewarded, whereas the very best non Muslim has no chance. The message is that belief matters more than moral behaviour.
And even many of those Muslims who do give to charity etc, do so for the wrong selfish reasons - to buy their own ticket to paradise, to look 'good' in their community etc. Bad motivation for good deeds is a human failing that will occur among the followers of any religion, or no religion. Look around you - Muslims are not immune.
Leaving aside secular morality - in what way is a person who does a good deed for the sake of their God any worse than a Muslim who does a good deed for Allah? They are equally selfless or self interested.
So, what it comes to is, you're saying morality itself is less important than belief. A Buddhist could be every bit as charitable, virtuous etc as a Muslim, but this counts for nothing. He gets the same eternal punishment as a mass murderer. There is only one punishment for any and every crime - and it's the worst possible punishment you can possibly imagine, infinitely exceeding the worst punishment man has ever inflicted on man.
And even a person of Mandela's exceptional qualities, or another like him, is potentially headed for hell simply because they were born into another religion, not a Muslim family.