It's common here to criticize Great Man Theory, in that it's not just one person that caused changes, it's many. However, where I'm lost is where they further imply that things happening have absolutely nothing to do with individual choice, and material conditions are the only thing that matters. This really just sounds like predestination with extra steps, as in, your material conditions will choose whatever actions you take, which completely loses me.
The logical conclusion to this mindset is that organization and trying to do political action is pointless, after all, material conditions will either make it happen or not make it happen, which I don't think anyone is trying to say.
Material conditions narrow the field of possible outcomes, but there's still some variation in the outcomes that are left. In some situations, that variation can have a big difference in the quality of life of people who have to live with the result, and people doing more than expected to organize can make a serious difference.