Also Dzogchen and tantric teachings do not require a monastic Sangha for support. During most eons when Dzogchen was taught, it was taught separately from any kind of sutric teaching at all.
This kind of dzogchen-centric viewpoint is problematic for a number of reasons, not the least of which is that the vast majority of Buddhists in the history of the Buddha's dispensation never heard of dzogchen...
So what? That is their lack of fortune. Now they have a chance to hear about it, and it they are interested, practice it. And from this Dzogchen centric POV, a monastic Sangha is not necessary for the Dharma. It also was not necessary during Sikhin's dispensation. He had no monastic Sangha. On the other hand, even though Buddha himself mentions Sikhin, etc. there is no reason for any contemporary Buddhist to submit to Buddha's mythology of the four or seven past Buddhas, unless of course they choose to.
and to this day this dzogchen narrative would not be accepted as authoritative by many (most) Buddhist traditions in East Asia and SE Asia.
Again, so what? This is just a question of authority and as we know, that lies in oneself.
Even in Tibet the historicity of the dzogchen tantras was questioned.
In India the historicity of Mahayana sutras were questioned. In Tibet, the historicity of Kalacakra was also considered suspect. Again, so what?
Therefore there is no reason whatsoever for any contemporary Buddhist to submit to this particular mythological narrative.
There is no reason for any contemporary Buddhist to submit to any mythological narrative of any kind other than personal choice.
Now then, back to what I was saying. When all is said and done, the only teaching that will be left and widespread will be Dzogchen teachings. That will be the Dharma which people will know and which will have survived. The reason is very simple. Dzogchen is the real essence of Dharma, the vehicle beyond cause and effect.