nyamssnanggong'phel wrote:So to summarize the errors of those who promote Tathāgatagarbha Sutras.
1. They don't understand all the normative ancient Indian professors like Atisha said Madhyamaka was the definitive sutra teaching.
Just to be fair: Longchenpa states very clearly in the sgrub mtha' mdzod that Prasanga is the definitive view, Tathāgatagrbha sutras are the definitive sutras.
Second, there was in India a broad group of masters who dissented from the position you ascribe. Recall, Atisha is very, very late on the scene and had virtually no influence on Indian Buddhism that is presently discernible, apart from being a younger contemporary of Naropa, Ratnakarashanti, Vageshvarakirit, and so on.
Also, Candrakirti seems to have left very little lasting impression on Indian Madhyamaka until Atisha's time, when his works began to be upheld with enthusiasm. This is evident by the controversy they eventually sparked, leading the composition of such texts as Ratnakarashanti's (Yogacara) Madhyamaka-alaṃkara.
2. They don't understand there is a difference between tantric Buddha Nature of Mahamudra and sutric Buddha Nature of Tathāgatagarbha Sutras.
Yes, this point is confusing for many people. It is made more confusing when scholars like Longchenpa regularly invoke the Uttaratantra in order to introduce concepts in Dzogchen causing people to conflate sugatagarbha teachings as they appear in Dzogchen and sūtra.
3. They don't understand tantra is higher than sutra.
Well, they can't be blamed for this since Sapan strongly argued against this position (indeed arguing against the position of his own guru, Jetsun Dragpa Gyaltsen). Since then, virtually all schools but Nyingma have maintained that the view of sutra and tantra is the same, differing only in means.