... And the size of the earth is irrelevant as the technology to move "small moon" size space stations exists in the cannon.
which really doesn't fill the plot hole. You're really just revealing a plot hole in the previous version that people just took for granted.
I'd assume that the StarKiller base has been equipped for moving with some form of propulsion and at great cost.
I think that would be out of reach for most other systems.
Plus then we would miss out on the great Millennium Falcon chase scenes!
Wouldn't it just make the chase scenes even more epic?