I suggest it should be changed from +0.5% defense bonus to just +0.5% weapons (multiplicative with your weapons%). So it retains its use defensively, but also works offensively. If you stack all your points on it, you'll reach about +30% by end of set. Useful for warring, but at least a good contender versus everyone just going for Turns all the time while warring. I'll even say I think +0.5% is too little.

(Believe me, If I'm sending 5m jets to PS you, sending 500k more is nothing to me. I see so many people on solo servers with Def bonus.)

Could also be useful for netting since it allows you to carry less units, spend less oil, giving a benefit much like a % reduction of expenses would.