Thanks for looking into this. I’m assuming then the Slash GraphQL product doesn’t support Relay natively and in order to comply with their server schema, this must be implemented by yourself. This is a shame as other back end services implement this for you based on your schema / database.
While Relay does look complicated at the beginning, I have found (as a Front End dev) it is a much better framework due to the reasons stated on their home page. GraphQL even links back to Relay for best practices (eg here).