problem.obj (333.2 KB)
even with a more right topology, you have those fillet thing with a weird shading
I tried playing around with the uv editor, or with normals, or redoing thousands of times the same mesh, but I get the same weird lighting/shading on the filled edges
It is because you have them in separate pieces. You should made the whole thing as one single mesh.
Merge the meshes together. 
but even if I make a single mesh there’s weird shading
uv editing it archives nothing
An obj file tells us little about your setup, generally it’s better to share the .blend file itself.
But just from looking I can see your UVs are probably not correct. If I just drop a simple Wave texture on your object at an angle to try and simulate something akin to what you seem to have there, it doesn’t work either.
Your UVs look like this – overlapping and going off in all directions:
They should probably look like this:
To get the textured object looking like this:
Just select all and simply do UV → Unwrap.
Here’s my test .blend:
problem maybe fixed.blend (1.6 MB)
I don’t really see any weird shading from the picture you showed? It looks more like bad UV, not bad shading.
The obj file doesn’t really show anything bad either in my side.
Still. Try resetting the vectors ( in Edit mode, select the whole mesh then Alt+N > Reset Vectors) and see if it helps. Maybe you did something that messed up the vectors.
