For smoothing by normal vectors at vertices → there is a topic in this forum about something similar and the solution was to smooth the object in Blender and reexport the model:
Striped shadows on OBJ/MTL model
Off-topic: I like @makc3d’s 4-points controls. I remember in the past I wanted to do something similar for one AR project, but I messed the math up and failed. I wish I knew this lib two years ago.