Just to let you know - CPU usage is completely different than GPU usage. I wanna spare the forum managers and the other members the wild-goose chase of trying to figure this one for you.
GPU usage indicates the utilization in a *positive* aspect of your graphics card, whereas the CPU usage indicates the processor's stress in a *negative* aspect. In plain words, ideally you'd want to have GPU usage as maximum as possible and the CPU usage as low as possible. It doesn't mean that the more CPU usage you are having the more fps you'd be granted as well just like the GPU usage works.
CPU usage is not an indication for a CPU bottleneck on its own, unless you actually hit the hard 100% CPU usage limit. But in your case, the CPU is indeed bottlenecking your GPU, but it has nothing to do with its usage, rather the fact that it's just the processor's limit. It's a relatively cheap CPU and BF1 is an extremely CPU intensive game (this is why you get 100% usage from your graphics card in other games, but not 100% usage in BF1).
As a matter of fact, if you look up benchmark videos of your CPU (R5 2600x) in BF1 on Youtube you'll see that the CPU usage in these videos is relatively the same usage as your CPU's. As a matter of fact this CPU would even bottleneck a GTX 1060 in BF1.
Even if you look up random benchmarks for the high-end CPUs on the market tested in BF1 you'll hardly ever see their usage going above 50-60% as well, unless they are streaming
