CGTC is ground texture-specific, aiming for a modern, crisp look with good performance with a focus on the terrain details. Where BARTHEK’s mod is a nearly comprehensive working to fix the entire environment (trees, lighting, water, etc.).
CGTC often emphasizes performance improvements with quality textures.
BARTHEK’s seems to focus on visual immersion vs. resource usage (this is a guess. I don't know either developer)
I am trying to understand @dlder's comments. I know basically nothing in this area and am still amazed by reshade and even just adjusting my Gamma LOL.