I think that crits do damage too. Same with adaptive armor. The extra damage is not really caused by the shot, but rather by small or not so small explosions on the ship. But i do not think that the damage from rolling just a 6 is going through, because i think it reads:
6: Solid hit, plus roll on the systems chart.
Besides GEG is stronger than you might think. Better than selfrepair actually.
GEG 1 reduces damage from EVERY weapon battery by one. WHEN that damage actually happens, not at the end of the turn. So in the case of a single weapon shooting, its works like this. 10 damage left, you take 10 damage, minus 1 ship survives. WS would be dead, cause self repair works later. ANd the more you shoot at ships, the better that GEG gets. Even t-bolts will rarely get 2 damage. Basically meaning that the GEG turns into self repair 5 or something.
Plus against fighters it is better than Adaptive armor. T-Bolts can ping WS to death. the crits still work on both cases. But the single damage hits of the fighters remain, the GEG just removes them.
Downside are huge weapon batteries and SAP Beams, which are just specialzed versions of huge weapon batteries.
Eg Abbai or Dilgar are good at killing Drakh because they have few weapon batteries, but those they have put out huge numbers of damage. reducing GEG effectiveness. Narn OTOH get waxed because they have many small batteries.