GPL would be perfect if it had "and, you are not allowed to exercise any other permissions granted to for this work except for ones granted by this licence, eve

GPL would be perfect if it had "and, you are not allowed to exercise any other permissions granted to for this work except for ones granted by this licence, even if you have separately received it or guaranteed by any higher authority, nor is the copyright holder allowed to grant such additional permissions to other such users." instead of "but it does not invalidate such permission if you have separately received it.".