"Uniform" means it has no small scale structures as I explained in my first post. Also I think what
@gadget271 said hits the mark. What I call "uniform" and gadget "flat floor" and "straight up" walls makes your stream look a bit like a man-made channel, not a natural stream made by natural erosion. In the picture you took for inspiration you can see al the irregular rocks and many different inclinations of the cliffs.
A problem is size of your new project. I said you should make is more narrow and you did that but you also made it much smaller in general. If you would have higher cliffs you could add more small details like side (lateral) ravines.
I still think you should make vegetation, stencils are essential part of voxel. Also adding stuff like moss covering the ground with plants like grass and moss (wall creeping moss from Gondor rp would be cool) using overlay and splatter overlay brush are important voxel skills.
I don't exactly know what
@BWOT want's to see for voxel badge. I'm just giving feedback on terraforming

But I really think it should
not matter for what purpose you plan to use a badge. The required skills should be the same for everyone.
Btw you wrote in your application that you want to use it for terraforming in general and Belfalas/Mordor in special
