Just wanted to come in and say that honestly I agree with you, we are planning to make the users-permissions plugin optional in the v4 and it won’t be installed by default however I personally believe that we could do better on this.
On that note, those specific fields are only used by the admin plugin as I assume you figured out and they aren’t polymorphic nor are they configurable without heavy modification to the strapi-admin package. Your solution is the correct one, I believe in the v4 we might be changing their name but I would need to confirm.