Following the discussion in the refleeting thread... offense would be most of your fleet, as a player, and defense, most of the turrets, mines, forcefields, and so on. Yes, if nitpicking, the flagship for example can have a great role in defense too. Yes, whatever is in the offense group can also help at defending.
Thing is that any mechanic meant to kill you as a player would have to bypass whatever your defenses while you're "weak", and that "you're weak" could happen if your offense is dead, or if your defense is dead, or both.
In starcraft, for example, I estimate the "power of offense / power of defense ratio" it to 5, if not more. Civ 5, would be closer to 1. AI war... depending on your unlocks... I think "my" playstyle makes it a 0.1 or 0.2 or something. Others with 110 -planet capture gamestyle probably run it toward 0.001, if not less. Anyway, in starcraft, when your offense is dead, you also are. But, if your defenses are dead, your offense can save the day. In civ, it's more of "the cities can hold" while reinforcement arrive - but against an assault, you need both (AI stupidity concerns aside). In AI War, of course it depends on the playstyle, but mostly... it does not matter if your offense is dead, you're still mostly safe.
Retaking the "define how the game finds out that you're weak" idea before, my opinion is that in AI war, you're weak when your defenses are crushed, and that the state of your offense is a minor concern when calculating your "can I be killed" ratio.
I think that moving back the "slider" to a position where offense is stronger than what it is now could be a good move. Plainly removing some defense options could work but I don't imagine it being very popular - which does not mean that cutting some options could be a good move anyway. Another idea would be that defense is more dependant on offensive units being present (ideas that would help with this could be manning the turrets with ships, or having planetary boosts to damage and range to the "defending offense fleet").
What do you think ?
PS: depending on ideas, "ultra defensive" gameplay could be kept as a mod / lobby option.
PS2: while they were "refused", I think some ideas behind platforms could be of use here.