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.
Aside from what other people here have already said, predestination is an opaque process where you can't truly know God's will until you die. Historical processes, on the other hand, follow natural laws that can be understood scientifically. In that sense they are quite different. One implies that the best we can do is hopeless mystification, while the other implies that knowledge is obtainable, and with it, power over our material conditions.