Field class has a .getProperties() method. Among the properties, “jsonSchema” will give you a JsonType object.
Using JsonType methods .getType() and .getCustom(), I am able to tell what data type the field is (including Insight fields).
There’s no solution to a generic setFieldValue() method though, but at least there aren’t a lot of system field setters, so I just switch on the field name and call each specific method.