The gun shield does provide heavy cover AOE reduction under certain circumstances (enemy throwing a grenade from a certain angle, and I assume this works the same for ballistic weapons) and the gun crew itself getting cover from the gun shield means that the other crew members will spread out, while the Raketen's crew will bunch up on terrain cover. So even if it's mostly bugged, having a gun shield does provide a significant enough advantage to weigh into the discussion.
So you cant fix the Rak being killed reliably by the thing its supposed to counter then? that's a shame. What about changing the crew to have a smaller size modifier so they are slightly harder to hit/insta decrew?
Are you able to fix the bug where you cant allow the Rak to move when cloaked (ie have it decloak, move, recloak) like camo'd ZIS/Paks can?