I am going to start by stating my understanding which might be wrong. My understanding is that mass cavalry charges did not really start until the high middle ages with the invention of the lance, high backed saddle, and stirrups. These knights were heavily armored and the horses had blinders right? My understanding is that it was a very unique type of cavalry that could smash into infantry head on right? Would the medieval heavy cavalry have been effective charging into something like a well trained Macedonian Phalanx or any truly disciplined and well trained force?

In earlier eras or in any other type of cavalry, I think that cavalry was used to harras, hit and run, and hit the flanks, or for horse arches.

Could the kind of cavalry that we see in the Ride of the Rohirrim have successfully charged into a mass formation? They did not look that heavily armored. The horses did not have blinders. I do not see high backed saddles. Would the horses get injured and the riders thrown from their horses?

We are having a debate about this on /r/fantasy. So I figured I would ask the history experts.