Why are the Green Suns power space based instead of actual reality warping, like Doc implied? And how does it exist before it was created to give Doc his powers and will those powers ever go away?

The Time in the Furthest Ring is weird, the Green Sun has always existed, but the Tumor was the thing that created it. It’s just that the further into the inky blackness of the Furthest Ring the Derse Moon went, the earlier in the Timeline of the Furthest Ring it went, with the detonation happening, arguably, at the beginning of everything.

Also, Space Powers are pretty reality-warping by themselves, being able to manipulate everything regarding Physical Space is. Nigh God-like.