What made me really understand this better than anything else though was playing "Mount & Blade 2: Bannerlord" (A kind of realistic medieval RPG, incl. a great Multiplayer option with Siege Battles etc.). In this game it's basically impossible to escape mounted archers in an open battle ground, especially when lured out of formation without a horse. It was eye opening for me to experience it in this kind of a way. A really lucky javelin throw or killing an attacking horse with an arrow to the head (when in range) could maybe save you. But in general mounted archers or armored cavalry would break the formation of front-line soldiers then attack them while circling around them, retreat when necessary, cut off supplies and basically terrorize the enemy on the battlefield until everyone is dead or has fled. Playing against other human players and not an AI gave it a very different feel too. Since winning strategies are abused heavily, which imo would have also happened in real-world setting, until the enemy strategies adjust to it.
There was an interesting write up in /r/askhistorians the other day, where they discussed military tactics of the Turcs and also Mamluks and other steppe tribes during the first crusades. Basically attack and retreat until the European enemies were exhausted from wearing the heavy armor needed for close combat.
- Also highly recommend a book from Yuval Noah Harari "Special Operations in the Age of Chivalry, 1100-1550".
The Book of the Five Rings and Richard Francis Burton's The Book of the Sword.
 - https://en.wikipedia.org/wiki/Book_of_five_rings
 - https://en.wikipedia.org/wiki/Richard_Francis_Burton
 - http://burtoniana.org/books/1884-Book-of-the-Sword/burton-18...