The old man had a very good grasp of his power, adjusting his own gravitational orientation must be the basic use of his ability, but it must have taken years for him to be able to move like that.
The "external" manipulation of gravity though... must have been something advanced that took even more time to conceptualize and master, maybe he really was externalizing his ability and creating a convergence point, or... he simply was able to extend his own "field" of influence far from his body but not detach it, it makes sense as an ultimate move and stays within the limitations Rami generally have before flowering.
And if I understood right... the fucker ability is somehow future vision, but not just that... the way his ability seems visualized to him, it looks like his "temporal coordinate" isn't fixed, somewhat like Zoe, he can see and maybe interact with the immediate future and react to it... but I don't know how right I am on that.
But it is a broken ability if used right one way or another... and this guy clearly has more knowledge of the world than he lets on.
When the authors decide to ramp up the fights in this... they go epic... the Heavenfall Ramus made me think of two things, first is Gravity Rush a PSP game where you could control gravity and the visual was very much like this, and the ability of the surge of gravitation in the Stormlight Archives book series, a user of it can "bind" themselves to a new gravitational axis like a roof and "fall" in that direction but with enough practice, they can make multiple "bindings" to create "pulls" of different strengths in various directions and "emulate" flight.