It's a made up statistic.

GraphQL reminds me of the NOSQL movement. Everyone wanted to try one of these systems, even when they were completely broken at the time (e.g mongodb) And yet, most apps will do just fine with a classical SQL DB and all the comfortable features you can use to speed up development at the cost of scalability (transactions, locks, listen/notify, etc). It's just not a pain point most app ever encounter.

Let me rephrase: How many times was the JSON payload bulkiness in the top 3 performance killers of your app? The answer is 0 for me, after developping dozens of apps. Although to be fair, GraphQL is not as extreme as the NoSQL movement at the time, as it's still a valid alternative even for some apps that are not at Facebook/Netflix scale and the very opinionated approach will be a comfort for many people compared to REST. I'm just strongly reacting to the "duh, of course you should use graphQL instead of REST" fad.