I literally doubt that, perhaps that could be the case in pre literate societies, but not so in literate ones. I think the jizya tax was the back breaker to non muslims, also the humiliation,fear.
I can't figure out exactly what you are doubting could not occur in literate societies, are you talking about military conquest and subsequent influence? I agree with you regarding things like the tax, humiliation and fear part, that is what I meant by influences beyond direct conquering and being forced to convert. As an ex-Muslim in the US, I can tell you many of those pressures (not tax off course) still exist.
There was no equality back then, we are using the present day ideas which come from last 2-3 centuries at most. I mean some of the greatest figures in the past believed there was nothing wrong with slavery. Not to mention slavery was accepted in islam towards non muslims.
I don't think you can see equality as all or nothing, because than even now we would have to say there is no equality (unless any of us is under the illusion that are treat people equally in modern societies). Islam offered many positive things to the very bottom groups of society at that time, which from our modern perspective are atrocious and violations of human rights but back than, it was a step towards better equality from previous non-islam societies in that region.
It really comes down to whether or not you have arms or not. In India, although the hindus had caste structure which was immoral, there was the class of warriors, who of course were always important, whenever muslim kings fought with each other. Having military is there fore a pre requisite as to ensure that one shall be able to defend ones views. If every non-muslim country around the world abandoned military in its entirety, then 200 yrs from now things would in my opinion be very different, there would be no free speech in most of the world.In almost every other place Islam went to, there was either no literature or people did not have soldiers to give them leverage.
I would agree that military backing is to some extent very helpful and probably close to necessary but not absolutely necessary. Islam itself started off without any military but later gained one due to attacks, which later became a way to conquer. I also want to make the distinction between what the islamic principles say about forcing conversions (There is no compulsion in religion) versus what muslims ended up doing. When I argue with Muslims, I always point out the fact that their religion may endorse the idea of no compulsion but they seem to think of it in a very limited sense of "I have a gun to your head, convert or die" and conveniently leave out the thousand shades of more nuanced coercion (some that you mentioned, tax, shame, guilt, group identity, tradition, family ties).