You could make more than one attack in Hollow, which meant more than one division/battalion needed to be kitted out for full combat. Frontier has basically all divisions on standby so you can choose which to full attack with.Encounter and defense battles had long since worked that way so I am not sure what you are talking about.
The game is absolutely merciful compared to Abyss.
In this game, all the deployed divisions fight nothing but encounter battles since recalling a deployed division to use them in a full fight makes no sense tactically.