originally taken from this Quora answer https://qr.ae/pGZzld
And later on, this:
It is a misconception that Muslims were lightly armored. In fact, heavy cavalry played an instrumental part in the Battle of Ain Jalut when the Mamluks defeated the Mongols.
Secondly, heavy cavalry wasn’t invincible as we see in the Battle of Agincourt, they might have been invulnerable to arrows but most of their horses weren’t which is why horse archers were also very effective against heavy cavalry; horse archers were employed to great effect by the Ottomans, the Mughals and the Mongols.
Plate-mail (plates interwoven with chainmail) was preferred in the Middle East and South Asia because it gave the protection of plate but was more mobile and lighter.