Maybe i can help clear this up. Watching Fujitora's powers closely, we can't call it the manipulation of gravity. Of course Oda could make up his own world's physics and we'll be here talking nonsense, but let's just base our arguments in what we know, which is our world's physics.
Gravitational force is the interaction between two objects. Forgetting the gravitational constant, it depends on the mass and the distance between those objects.
Now let's take Fujitora's meteor as an example. Meteors have a trajectory, which depends on a lot of things. But let's say that in this case the meteor is interacting with earth.
Object A - Meteor
Object B - Earth
If Fujitora were to increase the mass of the meteor, that would only cause the meteor to accelerate towards earth. This is because the meteor is free falling. Opposing forces like friction would try to decelerate it and slightly change the course, however, the impact spot of the object will not be too far from the original one. Fujitora making the object heavier is discarded.http://9gag.com/gag/aD32mZw?ref=mobile.s.cp
To change the course of an object that is free falling, you need and external force. I would assume thta his manipulating all sorts of forces.