One of the major misunderstandings here is that a gravametric device functions via gravity, this is simply not true. Gravity functions via a gravametric system.

Strictly speaking gravametric devices operate by bending the fabric of space time, gravity is one of the simplist manipulations since it just makes a hole but things like artificial gravity or antigravity are much more complicated since they have to make uniform deformations; then of course things like gravametric shielding is even more complicated because it has to make an intense but hollow sphere, and gravametric weaponry is even worse because you have to make a super-intense region, but if you just created a faux mass the field would consume a region that makes it ineffective as a weapon.

By definition warp drives and gravametric devices operate on many of the same concepts