I see an issue.

A prescription is enforceable if the sanction for not observing it is deemed realistically executable.

When you prescribe

exotic weapons may be utilized in the purge

You are basically stating "having exotic weapons is forbidden, and if you do, I will use my exotic weapons to punish you". This is a logical shortcircuit, because every signatory of the treaty will of course produce those weapons for the sole reason of punishing possible transgressors. Not having them will make the prescribed punishment vane.

The above logic is exactly what lead to the nuclear escalation between USA and USSR: I won't use nukes to attack, but I will use them if attacked. As you might now, it didn't bring to a non proliferation.