Gravity is an interesting explanation, but I don’t think it would work under the same principles as Lashings. Most of the time(I think) the object being pushed/pulled on still remains under the influence of normal gravity. Also, I’m not sure how gravity would explain how if the object you’re pushing on weighs more than you, you go in the opposite direction.
I actually have thought that the instability, how they vary in strength at certain points explained “flaring” your metals, as you could make that extra strong area towards the thing you’re pushing on. And it therefore takes more metal as it needs constant attention to make sure the strong side is always there.
As for the fact that it works in all metals, It might be that they usually affect those electro magnetic fields, but that with non-metals they normally can’t sense them, but the way metals interact with investiture makes affecting metal possible.
I honestly didn’t know that magnets could only attract metals, not push them away. Maybe it just slipped my mind. I don’t really have any thoughts for this other than that maybe, since there is something that attracts metal, there’s something that pushes it away, it would fit with the opposites theme of scadrial. I don’t really know though.
Any thoughts?