This is a topic debated since long ago. Many believe that the subfactions of MO3.3 cannot fit to a perfect S-A-I model. However in my opinion, they can, and they fit quite well.
Strength: Subfactions boasting significant HP advantages over its comrades. These factions utilize slow but heavily-armored and heavily-armed forces, and usually lack a real siege tank due to game balance.
Agility: Subfactions with well-rounded multipurpose units. Such subfactions trade armor for mobility while maintaining high firepower. These are token A-move subfactions and more than often related to the word "imbalanced".
Intellect: Subfactions which favor softening the target over providing units with more force. They are usually the most micro-extensive subfactions featuring fast units and various debuffs. These subfactions usually excel at harassment and hit-and-run tactics.