How would I model rocks like this?

I’m trying to model rocks for my game with a similar look to the rocks in The Witness. I assumed that they modeled High-poly rocks and then decimated them so they were more simple, but this process leaves me with a bunch of awful looking model errors, mesh problems, UV problems, and more. Is there another process I should be using other than modeling each face individually? Or is there a way to avoid mesh problems when I decimate?

The rocks above are from The Witness, by the way. These aren’t the troublesome rocks that I described.

With literally any 3d modeling program and enough motivation to make a rock.

None of the rocks shown even need uv mapping because they’re solid colors.

I can model a rock. I am having trouble modeling the more complicated, layered shapes. They aren’t as simple as they look and I’m very much a beginner. Thanks, though.