Interesting thesis, although his conclusion is overblown. Vijjā has a well established doctrinal sense. The fact that it can also be used in the sense of “mantra, mystic knowledge” is well known, and doesn’t change that. What is interesting is the specific use of the formula tadyathā … svaha which would be the earliest occurrence of this.
I tried to fact check a detail, namely the use of tad yathā in DN 16, or indeed anywhere in the Pali canon, and it doesn’t seem to be there. Anyway, it’s a straightfoward syntactic construction and in itself says nothing about a mantric use.
His citation of the “strange passage” is also imprecise; it’s not a passage at all, but some lines of verse from different places. The commentarial explanation is indeed forced, and the sense of the lines is unclear. It does appear that at least in part that these are perhaps garbled echoes of Vedic ideas. I’m grateful attention was drawn to these, because I formerly mistranslated following the commentary.
Paccesanto pakāsenti,
Tatolā, Tattalā, Tatotalā,
Ojasi, Tejasi, Tatojasi,
Sūra, Rājā, Ariṭṭha, and Nemi.
The first line should be, “Seeking, they shine”. The rest is a list of names. In such cases, best practice is to start by focussing on what is knowable. Tejasi is “brilliant, powerful”, and ojasi is “infused with heavenly nectar”. So these would be apt names for celestial deities, perhaps associated with the milky way.
For the last line, per my note, these are a set of associated solar names. Ariṭṭha and Nemi appear compounded in Sanskrit, Ariṣṭanemi, which evokes the powerful chariot of a conqueror (“indestructible rim”, Rig Veda 1.89.6, 1.180.10, 3.53.17, 10.178.1). It was the name of the 22nd Jain tīrthaṅkara, and in Brahmanical texts of several figures, including a dragon (Mahābhārata 1.59.39a, 1114.62a, etc.) and an Asura king (Bhāgavatapurāṇa 8.6.31, 8.10.10). Along with the divine steed Tārkṣya, he is associated with Garuḍa, and was probably originally an epithet for the unstoppable wheel of the Sun, Sūra. This line, then, while a simple list of four names in Pali, appears to be a fragmented memory of a Vedic conception which might be translated: “King Sun, (the wheel) of indestructible rim”.
Given this, while the names in the second line are still obscure, it is likely that:
- pakāsenti means “they shine” (rather than “they explain” per the commentary).
- The second line is probably another set of celestial deities.
As to the historical thesis, leaving other considerations aside, it is prima facie more likely that a passage with Vedic connections would be left out or garbled, and a passage of a more familiar mantric invocation would be added than the other way around. That is to say, this detail by itself suggests the Pali is earlier than the Sanskrit. It’s often the case that different parts of a text may be redacted in different ways at different times, so this does not mean that the Pali overall is earlier.