Still loved the movie-- I guess the director probably couldn't find riders ready to ride with those costumes without stirrups.
The Roman cavalry used to perform incredibly elaborate riding exercises while wearing gold and silver plated masked helmets with ribbons (and no stirrups).
Probably would strike us as a mix of the Lipizzaner stallions, Jason and the Argonauts, and La Cage aux Folles.
Stirrups weren't as bad as the repeating cross bow used in the Coliseum or the Roman soldiers who were wearing Blue Jeans