The bulk of WoW’s workload is mostly a single threaded (it will use a few more threads for some of the async workloads and other parts of the engine like sound). It’s basically always under a CPU bottleneck and there isn’t much that can be done to multithread it more, without having to rewrite half of the engine for it.
So let’s say WoW is loading ~4 threads and you have a 20 thread CPU, then you’d likely see HW monitors reporting something like 20% utilization. Note that if you look at the task manager graph of CPU threads, you’ll see activity on a bunch of threads, but that’s just the Windows scheduler min/maxing things and spreading chunks of the threads around to load level.