Y'all are right about variables when it comes to lag.
I believe FH is a game that only makes use of 1 core from the cpu, so even a good gaming rig for other games may be a terrible choice when it come across a program like that. It also depends on your RAM, I recommend 4GB for FH. I'm not sure if FH makes use of any dGPU's and if you've got less than 1GB vRAM on your iGPU then it will also probably be a cause of lag...
But yes, the game itself is also a cause due to some of the limitations of it. ie: 1 core vs all cores.
Edit: oops, double post.. my bad. xD