Yes, basically. Some workarounds come to mind, but they’re not “nice”.
One option may be to install the Simple JSON Datasource (https://github.com/grafana/simple-json-datasource) and set up your file in S3 so that a request to https://your_s3_url/query returns a JSON payload that that plugin can parse (see the link for an example). Though that may require some major rejigging of your JSON.
The load-from-CSV option is discussed here: CSV file as a datasource?