Sounds like you could have made your feed items REST API return the top 3 comments as well...
Maybe the lesson here isn't that GraphQL is a magic bullet, but that designing your API for your business needs solves a lot of frontend complexity (even if it's not pure "REST").
Maybe the lesson here isn't that GraphQL is a magic bullet, but that designing your API for your business needs solves a lot of frontend complexity (even if it's not pure "REST").