I think you're confusing 2 things. The "energy of a field", whether that's a magnetic field or gravitational field is fictional. It's potential energy. In orde

I think you're confusing 2 things. The "energy of a field", whether that's a magnetic field or gravitational field is fictional. It's potential energy. In order to move from A to B you must "pay" the difference in potential energy between the 2 points in space. That payment can be negative (e.g. falling). So if gravity increased in strength after ~2000 light years (which is the problem dark matter tries to solve) to 1/r instead of 1/r2 that would not represent any energy at all. It would not insert energy anywhere, into any particle, it only changes the "fictional" values of potential energy in a bunch of locations. Therefore it would not violate conservation of gravity. Oh, and things form discs by default. If things fall into something, they form a disc shape. Round things are only formed once the collisions between stuff in the disc start going over a certain level. Galaxies are so incredibly low-density there are even a few galaxies that have multiple discs, but still very much discs. Only "small" things are ball-shaped, like stars and planets because the particles exert pressure on each other and the third dimension provides a way to relieve the pressure.