At the moment the rest sensor only supports the json_attributes in combination with json_attributes_path config. This is a bit restricted because all attributes have to be located in the same object. There is an example in the docs which works around this by creating another template sensor which extracts the values. But I think a better solution would be to support templating in the attributes of the rest sensor directly. Additionally I don’t know another integration which uses the JsonPath for configuration which makes the configuration a bit inconsistent.
Agreed
It also would be helpful to be able to use templating to perform operations on the attributes as they are set - eg converting data to a date