No, a list can only have the same type entity. Is there a reason why you don't want to use a loop?
Is it a possibility to make the JsonObject_C persistable, and store your products in that table?
That way your saved products, and recieved products from the rest call are in the same entity, only those from the restcall you don’t need to commit. Adding a boolean or enumeration to the entity could then easely tell you if the object is one from the restcall or from your database
Have you tried adding the retrieve to the import mapping?
Maybe in that microflow you can retrieve and a merge your persistant objects into the received JsonObject-list.