It would make sense to be able to restrict the objects that you see linked to an object, depending on the function of the object itself. For example, if you have a Custom Object name ''X'' it does not make sense as a user to see on the right panel side the option to create a custom object ''X'' again. It's confusing for the user, as they are easy to believe they are in the wrong page.
Is there a solution in this that I am not aware of?
To return only defined properties, you can use the properties query parameter. For example, the following request will return only the defined properties for the companies object