The two are not exclusionary. For me it is like having a higher abstraction API that provides for 80% of client developer needs, and a 'closer to the metal' AP

The two are not exclusionary. For me it is like having a higher abstraction API that provides for 80% of client developer needs, and a 'closer to the metal' API that provides for the remaining 20%. REST gives the popular/frequent queries optimized and canned, while GraphQL gives the power to create completely custom adhoc queries as needed. If you are creating a data service then I think you really need to have both. Which you do, and how much of it, is more likely to be dictated by time and budget. Many will need to figure out who their 80% audience is and prioritize based on that. Still a few REST services can be done, then GraphQL added with not mutators, then add mutators and more queryable data, etc. Start with the bare bones, just like you would a startup MVP and grow organically from there.