For what its worth, off type defense isn't actually stronger, it is just almost as strong as on type defense. Lets look at two quick examples:
Say you face a 50 pt defense, and your weapons do 10 per turn.
On Type:
Attack 1 = Def reduced to 40 [0 damage done]
Attack 2 = Def reduced to 30 [0 damage done]
Attack 3 = Def reduced to 20 [0 damage done]
Attack 4 = Def reduced to 10 [0 damage done]
Attack 5 = Def reduced to 0 [0 damage done]
Attack 6+ = doing damage.
Off Type: Def = sqrt 50, or 7
Attack 1 = Def reduced to 43 (so def 6) [3 damage done]
Attack 2 = Def reduced to 37 (so def 6) [4 damage done]
Attack 3 = Def reduced to 31 (so def 5) [4 damage done]
Attack 4 = Def reduced to 26 (so def 5) [5 damage done]
Attack 5 = Def reduced to 21 (so def 4) [5 damage done]
Attack 6+ etc.
While you have knocked out all of the defense under scenario 1, you have done 21 more damage against the off type defense. It takes more attacks to knock it out, but it also blocks less damage. The above is a simplification (no randomness to the rolls), but the basic point is that 50 is still greater than 7+6+5+4+3+2+1. The problem is that you would actually have expected to do 43 damage against the off type defense, but you only did 21. This effect magnifies as your attack and defense numbers approach 1000, but off type still consistently blocks
slightly less damage than on type defense.
In any case, I do hope a fix is forthcoming. And yes, I believe that every version of DA had this bug, so to get around it you would need to go back to DL. Even in the first version, people who made large defense oriented ships were reporting that they were performing very well. When the cost was lowered and everyone began using defense, it just became much more obvious that this bug existed.
Good luck to all, hope that helps.
