As a frequent user (and abuser; my current 2000 point list can put out 70 Grav shots a turn) of Grav Weapons, I know how over-powered these weapons are in the current game and agree with many that, when 8th edition comes around, GW should find a way to make this a less “auto-take” weapon and rebalance how they fit into the overall game. Right now, if you really want to be competitive, no other weapon choices really come close (the DW Frag Cannon might be an exception, but even that is not as strong against so many targets as Grav Cannon/Amps are). Additionally, Grav weapons are pretty much single-handedly the reason that lots of iconic units like Terminators, Land Raiders, Dreadnoughts, etc. are rarely used in the current competitive meta… thus, toning down Grav might allow for a “rebirth” of sorts for the competitive use of some of these units.
Now, Grav weapons do bring one positive to the game, namely they are a hard counter for things like Wraithknights, massed Riptides, massed Dreadknights, Stormsurges, and even certain types of Deathstars that would otherwise be almost impossible to deal with. Taking that into account, and considering the other heavy/special weapons available to armies with access to Grav weapons (i.e. Plasma weapons, Flamer Weapons, Melta weapons, Missile Launchers, etc.), I think the following might be a possible solution for “balancing” out Grav weapons so that they still have a purpose and can be taken in competitive armies, but that they do not overshadow all other weapon types and make certain units unplayable:
—GRAV WEAPON PROPOSAL—
*Grav Weapons would still maintain their current profiles, including number of shots, range, AP2, and Concussive rules.
*Grav Weapons would not longer strip a HP from and Immobilize a vehicle when they roll a 6+. Instead, on a roll of 6+, they cause a Crew Stunned result ( with NO hull point stripped).
*Grav Weapons would no longer wound based on the target’s armor save (i.e. wound on a 2+ against TEQs, on a 5+ against GEQs, etc.). Instead, they would wound according to the following chart:
T1-T3: 6+ to Wound
T4: 5+ to Wound
T5: 4+ to Wound
T6: 3+ to Wound
T7-10: 2+ to Wound
**Note: If the target is a Monstrous Creature or Gargantuan Monstrous Creature, then reduce the roll on this chart by -1 (so a T6 Riptide would be wounded on a 2+ and a T5 Daemon Prince would be wounded on a 3+, for example; this would not be able to improve Grav Weapons wounding to better than a 2+, however, so if they were a MC with T7+, then they are still wounded on a 2+). Also, Flying Monstrous Creatures/Flying Gargantuan Monstrous Creatures suffer a -2 to any grounding checks they take if they suffer an Unsaved Wound from a Grav Weapon that same turn.
So, you can see significant proposed changes here. Overall, the idea is to make Grav weapons still very strong at dealing with MC/GMCs, and even a solid counter against higher toughness units like Bikes, TWC, Nurgle Marines, etc., but also to make them vastly less powerful against standard infantry and vehicles. The vehicles, in particular, would no longer lose HPs to Grav weapons and, at worst, be unable to Move and Shoot for a turn (I think this gives you the ability to still use Grav weapons on vehicles as a “desperation weapon,” but not make them the go to choice over plasma, melta, MLs, etc.).
If these changes were made, I think you would still see armies taking Grav weapons, but in much smaller quantities and for much more specialized “monster hunter” duties, rather than as a staple for the entire army list. I also think you would see an uptick in plasma and melta weapons again, since they would have to step up to fill anti-MEQ/TEQ/vehicle void resulting from the Grav weapons being rebalanced.
Also, as I alluded to earlier, I think expensive, elite infantry and vehicles (like Land Raiders, Terminators, etc.) would start being more useable again, since they would be so much less vulnerable to Grav weapons than they used to be (i.e. under my proposal, for example, it would take 6-7 BS4 Grav shots to kill a Terminator on average, whereas before it only took about 2-3 BS4 Grav shots to kill one). Finally, I think Grav weapons would still have an auxiliary role because of their Concussive rule, which enables them to debuff multi-wound models before charging into combat, and also because of their ability to help bring down FMCs, since they have a much increased chance of “Grounding” them.
Overall, this would not fix all the balance issues in 40K by any means, but I think it would go a long way toward bringing competitive lists back toward “center” and allowing more diverse units and weapons to be included in those competitive lists.