So they need to blend both modes/tech into each other.Fortress mode can be used more offensively. The Ablative Batmobile armor is just the ship turtling until the threat goes away. Fortress mode is Leroy Jenkinsing into a situation, pulling all the dangly bits in, and firing everything it has in every possible direction for as long as the reactors will allow.
So you can armor up and fire everything at the same time =D
And have Shields + Armor + Weapons & LeRoy Jenkins your way into a fight.