I'm saying three things:
1. Buddha Shayamuni/Buddha Vajradhara did not teach Dzogchen - his teachings are the Sutras and Tantras. These teachings are a complete system that lead to liberation and enlightenment by removing all mental obscurations.
2. The true nature of phenomena is emptiness, lack of inherent existence. There is no attainment of enlightenment without realising this because grasping at its opposite is the cause of all mental obscurations.
3. There is no path to higher attainments that doesn't depend upon meditating on emptiness. The meaning of emptiness was explained by Buddha and reiterated by Nagarjuna and Chandrakirti.
In an attempt to have a discussion, I will reply.....though I anticipate only some sort of rote NKT-formulaic response:
1.Many dispute that the Tantras were taught by the Buddha. Surely you're aware of this. Vajrayana is not accepted Dharma in many Buddhist traditions. In fact, Malcolm has provided one instance of a "pro-tantra" authority who disputes a given specific instance of this.
2. Ignorance is the root cause of all mental obscurations. If one is attached to emptiness, and sees it as the "opposite" of existence, then one is still mired in the thicket of concepts, however subtly. Although it's fair to say that grasping is certainly part of one's bondage, we can also say there is no "opposite" of emptiness to be grasped in the first place. There is, first of all, merely a mistake. Grasping comes after. It's not a matter of choosing one side or the other, in the end, but a matter of freedom from extremes, and transcendence of conceptual activity.
3. There are many methods of practice where "emptiness" is not the primary object of meditation, and some assert that "higher attainments" can indeed be had by such methods. Certainly, understanding "emptiness" is not a bad thing, we can even say "emptiness" is a factor of many systems, but Dzogchen and Mahamudra, as well as the completion stage practices of Highest Yoga Tantra, do not take "Emptiness" as the primary subject or object, a la Nagarjuna, Chandrakirti, etc.