Operating system: Windows-7-6.1.7601-SP1 64 Bits
Graphics card: GeForce RTX 2070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 431.60
Broken: version: 2.80 (sub 75), branch: master, commit date: 2019-07-29 14:47, hash: rBf6cb5f54494e
Short description of error
Geometry can appear very "faceted" at the extreme edges of curved geometry - where the angle of the normal approaches perpendicular to the light.
I've been seeing this for a while, so, it might be a known issue. I spent a few hours trying different ways to eliminate this, and while using Adaptive Subdivision will work, it isn't ideal on meshes where subdivisions will affect the shape too dramatically.
I ran into a similar problem a while back using Redshift - they believed it to be related to their shadow bias algorithm ( https://www.redshift3d.com/forums/viewthread/8035/#51073 ) - and eventually, they dialed it in to where I never saw it again.
Exact steps for others to reproduce the error
Open the attached .blend file. Render using Cycles.