(...) I struggle to find examples of infantry falling back in good order in front of an enemy in accounts of ancient battles. Caesar attempted it in Gaul and it went badly wrong... (...)
I think you shouldn't use such argument when it is in the main game...
Especially that most of us here surely know the "inverted crescent" tactics, which is exactly falling back with the center infantry under the pressure of the enemy to draw him deep and then encircle from the flanks with cavalry.
But even if you wouldn't want to simulate the famous Hannibal moves, then fall back is a tool that greatly helps correcting mistakes in deployment. It was during my second Pacto battle that I thought "WTF I can't fall back with my infantry?" It's not a simplification - it's a bug. ;-) Which puts newbies into irreparable situations.
You know - if someone went through the whole rulebook, his brain didn't melt and he still wanted to play the game, then he would surely be able to comprehend such simple rule.