GPUs really just aren't designed for 2D vector graphics. There is a litany of approaches (three separate ones from pcwalton's Pathfinder R&D alone), and all of them have various issues and tradeoffs. If your GPU has enough power for one of the more advanced approaches like Slug or Pathfinder1's compute shaders, then your CPU likely has enough for Blend2D and the bandwidth for the resulting texture upload.

Pathfinder3 looks promising, but comes with its own tradeoffs. It's an open area of research.