I’ve never experienced anything like that on my more modest system (i7 16GB RAM; RTX2060 GPU).
It would help to work out where your bottleneck is if you could re-record that with the Windows Task Manager “Performance” tab showing the realtime usage of: (a) Hard discs; (b) SSDs; (c) Network uploads and download throughput; (d) GPU usage percentage etc.
And what setting is your “Off-Screen Terrain Pre-Caching” set to? (If set to ‘High’ or ‘Ultra’ it will cause the GPU to throttle back on my system)