The headset does have it's own GPU and CPU, but it doesn't assist the PC in any way. In fact using a Quest will have a slight performance drop compared to a Rift or other brands like Vive/Index. This is because a Rift or Vive directly pass the raw game gfx over a video cable, while Quests require the PC to compress the video into a stream which adds an extra hit to the PC's GPU.
Also a Quest 3 is significantly higher resolution than a Vive or Index, so there's a bit more overhead if you want to really take advantage of what it can do.
So I guess technically a Vive or Index will give you slightly better performance, mainly because they are lower res devices. (Quest 3 is 2064 x 2208 per eye, Vive is 1080 x 1200 per eye, Index is 1440x1600 per eye)