I argue that the proposal in question is complete duplication of CoCR. Yes, CoCR is broad... but so is this proposal. And it is not just partial duplication, the proposal adds nothing that is already done by CoCR in its first three clauses:
a) All inhabitants of member states are equal in status in law and under its actions, and have the right to equal treatment and protection by the nation they inhabit or in which they are currently present.
b ) All inhabitants of member states are entitled to rights secured to them in international law and the law of the nation they inhabit or in which they are currently present.
c ) All inhabitants of member states have the right not to be and indeed must not be discriminated against on grounds including sex, race, ethnicity, nationality, skin color, language, economic or cultural background, physical or mental disability or condition, religion or belief system, sexual orientation or sexual identity, or any other arbitrarily assigned and reductive categorisation which may be used for the purposes of discrimination, except for compelling practical purposes, such as hiring only female staff to work with battered women who have sought refuge from their abusers.
So we see CoCR already prevents discrimination on the grounds covered by Against Political Discrimination, which covers any personal matters (which would be arbitrary and reductive categorizations), including sexuality and religion which are specifically mentions in CoCR. Against Political Discrimination does not add anything new to International Legislation, and should it be held legal it would open the door for a million CoCR clones: "Against Hiring Discrimination", " Against Discrimination Against Racial Minorities", "Against Arbitrary and Reductive Categorizations", etc.
Additionally, I also argue that Against Political Discrimination contradicts CoCR, which explictly allows discrimination for compelling practical purposes, while Against Political Discrimination prhobits discrimination totally, not allowing for compelling practical purposes.