Good question pbowyer! We actually do a bunch of GraphQL parsing / calculations in the Compute@Edge layer. So without that, we would not be able to provide our current features.

We also support a feature we call "scopes" - where we both support cookies and headers in the "Vary" header so you can cache user-specific data only for the user with a specific "Authorization" header for example.

In order to support scopes with cookies, we needed Compute@Edge and could not make that work with VCL on its own. But believe me - we tried. Our first version was actually mostly built on top of VCL.