Stirrups are among the more forgivable historical inaccuracies, as it is difficult enough to find people who can both act and horse-ride with them reasonably well. Also, if the depiction of cavalry was more historically accurate it would matter a lot less.
replyThe Mongols really learned to work with them.
replyI’m pretty sure that stirrups have been crucial to cavalry tactics since they showed up in Europe (I think around the Dark Ages). Being able to stand up in the saddle was certainly important to lancers.
Of course, horse training was also important.