Customize your SharePoint Column, View or Form Layout Formatting JSON using a full-featured editor instead of the default one. Supports Google Chrome and Microsoft Edge (Chromium). If you have SP ...

area:list-formatting Category: View, row & column formatting with JSON type:bug-suspected Suspected bug (not working as designed/expected). See “type:bug-confirmed” for confirmed bugs.

And actually, I may be able to get the guy who put together that web service to format the output as XML if getting JSON requires workarounds.