[jmagoon]

That's just really not true based on modern research. That's a fringe theory at best, that might be applicable to something like "Mainstream Buddhism". (e.g. what you see in a yoga magazine in the grocery store)

There's quite an established corpus of Tibetan texts and monastic curriculum that has existed for the past 1000 or so years (depending on the tradition) that involve primary sources (Sanskrit Indian texts dating from 100 AD or so onwards) and developed commentary in Tibetan. It's of primary importance for every Monastery / center to have a full set of Kangyur (sutra) and Tengyur (tantra), with many of the most revered and most studied texts coming from 1300 AD or so in Ancient Tibetan, and as far back as 100 AD (Sanskrit and Tibetan translations of Sanskrit).

There is meticulous textual preservation practiced at all major Tibetan monasteries, and many have preserved texts throughout the Cultural revolution that have been confirmed by other discoveries of identical copies and translations in China, India, Ceylon, and Southeast Asia.

That's an extremely odd theory, as well, because Tibetan literally has two different forms: Modern and Ancient, and texts can be dated by their use of language, similar to Modern and Ancient Chinese, and anyone who denies that is basically equivalent of thinking fossils were buried by the Jews or the earth is 5000 years old or something equally non-factual.

It's certainly reasonable to say that there are "Buddhisms"--there were many different interpretations of primary sources in different Asian regions that continued to develop independently of each other (and merged with local custom or ritual), but it's somewhat ludicrous to say that there was "no core set of ideas" that was being actively practiced in Asia 150 years ago within specific traditions, or that what is currently practiced in Asia is "Western" at its core. You can even make a strong argument that there are a few core principles that are consistent across all branches of "Buddhism" that have little to do with Western ideas or Western religion, namely lack of self, and the composed nature of all phenomena, which have their roots in the very earliest texts, with constant development and reinforcement from ~100AD forward.

source: Master's in Religious Studies, specifically Tibetan Buddhism

[Alex3917]

The argument is that it's the primacy of the ancient texts and practices that is recent, not the texts and practices themselves. (Again I'm not a historian, but nothing I've read or heard leads me to suspect that this is some sort of fringe theory.)

[jmagoon]

It's hard to argue, because you could pick up literally any textbook on Buddhism to see this is a fringe theory.

If you are actually curious about this topic, I would suggest you look up the importance of lineage in the Tibetan, Chinese, Vietnamese, Korean, Mongolian, and Japanese traditions. Warm hand to warm hand, as it is called, is extremely important. Lineage is legitimacy, and it's always the first line of defense against charlatans. That means that the most important thing in those actual traditions is where a practice comes from and who the teacher is (and their teacher, and theirs, etc.). It's even fair to say that the de-emphasis of lineage and tradition exists only in "Western" or "Mainstream" Buddhism.

If you're curious, Buddhist Geeks has long been far from the academic mainstream and has more recently gone much, much farther out.