OK. I think I found the solution. Long story short: Set Max Framerate
After setting max framerate in game to 90fps (GPU fps in top right dropped from 130+ to 90+, relative to my last screenshot), Client Frame Time (CFT) dropped from 19 to 10 and Time Nudge becomes low and stable.
After discussing with AI, it mentioned my CPU (R7 4750G) had relevant small (8MB) L3 cache. Because there were massive frames to process in a sec, L3 cache might suffer from low cache hit rate. This make CPU need to access data from RAM frequently, which caused the delay. As CPU was "waiting" data from RAM, it's not fully occupied. This explained why my CPU usage didn't elevate to 90+%.
While max framerate is set, it reduce the number of frames need to be processed in a sec, and therefore increase cache hit rate. Now, while CPU doesn't need to access data from RAM that frequently, CFT decreases and so does TN.
I don't know if the theory is correct or not with my limited knowledge in computer architecture. Maybe it's all AI **bleep**. Max framerate just mitigates some micro-burst issues in my CPU.
But it does work.
