Interactively querying REST APIS is a massive pain, doing anything useful requires multiple dependent queries, postman doesn't really help with that.
Being able to query a graph interactively is actually useful, I've used graphiql to explore the data graph to figure out the query I need for the data requirements of a component before I start writing the actual component itself.
That really depends on your API! We have an orchestration layer that exists specifically so our front end does not have to run multiple queries all the time. Most of what our front end does is by running a very small handful of queries.
I think orchestration layers are something most growing/larger orgs strive for, in my experience.
If it's actually a REST API then it's going to take multiple queries. Certainly you can put an non REST API in front of it to reduce the queries. Every site does it and every site does it in a different way. GraphQL is built to solve this exact problem in a standard way.
We use postman extensively at work. We even have non-devs using it to hack with API's to get things done without having to wait for a UI to be built. It's a great tool. I especially like how you can serialize all of your saved endpoints and send them to other devs.
