It is more the net code and server tick rate than the CPU core usage. Total CPU + GPU render time is well within range to maintain 60fps but something blocks the render thread for too long before it starts building the next frame. This is most noticeable in cities. PvP has additional issues. Profiling was done with GPUView and XPerf to show this.

No excuse though. It's a question of inefficient net code and not enough server resources. Most people have come to expect mediocre performance from mmo's.