What settings are you using? I tried it on both my PC systems and the stuttering is bad on both. I can get second-long pauses when flying around on a planets surface. Even in space, where it does manage to hit 60fps, there's regular hitches in the framerate.
It's unbelievable to see how smoothly it performs on PS4 then see how bad it is on PC. If it isn't broken in some way then it must be really finely tuned to the PS4 hardware.
I'm gutted about it to be honest. I know I still have the PS4 version to play but it was the PC version that I was most looking forward to because of my preference for playing first-person games with keyboard and mouse but I can't play it in this state.
That's what I ended up doing while trying the game. Keyboard and mouse controls for flying are rubbish.
Edit: This was posted by a dev on Steam:
Edit 2: turning off shader caching has stopped the pauses I was getting while flying.