I don't think I have played WoW with my 7700k, but I know on my i7-4770k major towns were still a kick in the teeth to the CPU. I could easily achieve ludicrous frame rates in dungeons and the general overworld. Large raids were noticeably slower, but still plenty fast. 50FPS is not unreasonable for raiding.
The main thread, which runs on a single core, basically handles the netcode and all the player data handling. Each player position, spell effect radius, armor/damage calculations, etc. It really adds up quickly the number of things the CPU has to do to tell the GPU what to display on the screen.
So basically what you're saying is that I can't do anything bar upgrade my CPU?
And yeah it runs the same regardless of the settings so if you're right then I do have a bottleneck.
Is there anything I can do in that scenario?