It appears that it is no longer possible to assign unit types into different formations. An effective strategy I used to use was having my shieldless line breakers in a separate group to outflank and envelop infantry once the initial fighting had begun, though now It appears this cannot be done...
This is nearly gamebreaking for Vlandia as they will not use their shields half the time in a shield wall, and will punch enemies in melee range, making them useless in sieges once enemies breach the walls.