Plot this, Plot that....
You can do whatever you like in a campaign to fit your own vision in the FS universe and still making it seem plausible.
IE you can introduce a new prototype of fighter which has not been completed and send the pilots out to test it without shields, or you can say your fighter need so much energy drained to the main guns and/or other subsystems that makes it impossible to the reactors to sustain a decent amount of energy output to fill the shields requirements.
Still, I know INFA's missions will most likely not feature unshielded fights, but well... I was just excited about the idea.