My understanding is that your schema.graphql should be much simpler then the generated prisma.graphql. You should only expose the information that is needed.
Personally, I've overridden about ~200 lines in my schema.graphql. So I copy and paste big chunks into my schema.graphql.
I imagine an alternative is to have your own generated schema.graphql. Checkout
https://www.apollographql.com/docs/graphql-tools/schema-transforms.html if you take that approach.
Would be happy to hear what others are doing as I'm guessing some best practices will develop.