From Mahayana to Vajrayana (and Dzogchen) what you have is an increasingly global synthesis of Buddhism and Vedism. Once the method of anapanasati is changed from a mindfulness method to focusing on the breath as an object, then one begins to enter into the genre of practices begun in Pre-Vedic ages of focusing on objects, like mantras, images, etc., which are in essence a manner of concentrating on vibration.
Then, it becomes natural to synthesize Vedic ideas that flow from such experiences, like Brahman in Sanatana Dharma. How the Dharmakaya is a species of Sanatana dharma is where in Mahayana and Vajrayana the seed syllable is said to emanate from the Dharmakaya, as in the case of the Prajnaparamita of a Single Sound, etc., where mantras and dharanis become used. This comes from an Upanishadic notion about the nature of AUM. The Dzogchen Tantras explicitly describe themselves in the same way the Vedas describe themselves, as emanating from the primordial origin of the universe, namely sound.
Here we have a line in the sand. In Vedism you are focusing on vibration. One is supposed to trace the vibration back to the origin and find Brahman. Whereas, in Buddhism you are mindful of breathing, etc., to recognize pure consciousness without surface or feature with is Nirvana, no vibration. On paper it is not possible to discern, but having practice all three of these systems for years I discovered that the place in ourselves where vibrations emanate is a courser level than the level of pure consciousness. Brahman is the level of dreamless sleep, unconsciouness. Become aware of that is not nirvana which is completely lit and never unconscious.
Also, the Sravaka method of anapanasati is very fast and leads in a matter of days to whichever result Vajrayana and Dzogchen says takes a whole life or more. They are dragged down by these vibration concentration schemes. Even Mahamudra and Dzogchen in their pure forms, meditating "on emptiness," are dealing with the level of mind and thoughts, where they arises and disappear. This is not the path to nirvana either. You are still dealing with the level of fluctuation. In a real sense, these methods incorporation of Vedism and the use of such types of methodology, invariably leads to the Deva realms and not beyond samsara. It is their views about not the extreme of nirvana and not the extreme of samsara that keeps them in samsara.
Subsequently, I realized the explanations in Mahayana denigrating the Sravaka introduces doubt about the Sravaka's method and prevents success in that method due to that doubt. Which means Mahayana is hindrance.