In my experience GraphQL slows down all teams. If you're on a new project and that's the stack you pick it can work well for a while but as soon as your product is large enough you get multiple GraphQL api's built by different teams that don't behave in a similar fashion. If you're in an org with historical code now you've got APIs that are RESTful and then some which are GraphQL based. Making those work together is either a hack on the frontend or a rewrite project.

Ultimately the thing that speeds up teams, again in my experience, is predictability not flexibility. If you tell someone they have a RESTful API they know exactly how to work with it, document it, etc. GraphQL which is shiny, new, and used by in-vogue orgs is fine, you can use it to get the job done, but I don't believe that it warrants much praise.