there will always be some amount of bottlenecking. ur 1600X and 1070 just has a minimal amount.
see the cpu usage while gaming and that will tell u if ur 1600X can be pushed further with the 1080.
monitoring cpu/gpu for different eye candy settings can also give u insights abt GPU/CPU performance saturation. like the cpu usage can be the same for high or ultra presets means the game is GPU dependent and can be pushed further via a better GPU and vice versa.