That is excellent, I love your approach to legion command and to the strategic and tactical gameplay (deep enough to be engrossing, but simple enough to not detract from the fact that this is an RPG and not a 4X game).
In terms of mechanics that would allow us to influence the outcome of battles beforehand, I can suggest a few ideas:
- Diplomacy, e.g. trying to get parts of the enemy army to defect or desert. Sow discord within the enemy army. These can be done in-character or you can send centurions on missions to attempt to do this
- Assassination/sabotage, e.g. assassinating officer