FH4 vsync cause low gpu usage???

I’m having a really weird problem on my pc
Lenovo y50-70 touch
Core i7-4720hq 2.6ghz
16gb ram
500gb Samsung ssd
Gtx 860m 4gb

In most games like gta I can run on high to ultra settings on 1080p on 40-60 FPS but I noticed that on horizon 4 I can barely Run on medium with low streaming bandwidth errors.
I did some checking and I saw that when I play on medium with automatic optimization and vsync on I get only 27 FPS but the gpu and cpu usage in only around 50-70%???

Tho when I turn off vsync suddenly the usage of gpu go up to 100% and I get 40fps … also when I change the resolution from 1920x1080 to 1920x1440 the usage go up and the FPS too…
what’s going on???