I wouldn't let that sway you too much; the main reason for the performance difference is that PostgREST builds the JSON response in the database and then pipes that through to the user directly (at least that's my understanding). PostGraphile OTOH parses the JSON from the database and feeds it through the rest of your GraphQL schema, allowing data to be mixed in from your custom fields which might fetch from microservices or external services such as Stripe, or just perform additional calculations in application-land, and finally serialises the resulting data to send it to the end user. Despite this significantly greater flexibility and power requiring all this additional work, PostGraphile achieves very solid performance.
came here to suggest the same thing :) I have been using this project and contributing to it recently and it is really great.
It has been months, and I keep discovering possibilities and functionality :)