I have no desire to challenge your superior understanding of Tibetan Buddhism as taught to you.
My point has always been that the faith has many aspects.
Perhaps an analogy will help. In the Church of England, for many centuries there were Low Church and High Church tendencies. The Low Church varied all the way over towards Calvinism, while more extreme versions of High Church Anglicanism were very nearly indistinguishable from Roman Catholicism.
In fact, throughout its history the COE tended to leak individuals and groups in both directions, as they became too far from the compromise position held officially by the Church.
This is with a Church with official dogmas, creeds, statements of faith and all that. I suspect Tibetan Buddhism varies at least as much, since I believe it lacks any such formal statements of doctrine.
Your suspicions are incorrect. Analogies to the evolutional history of Christianity are tempting but not valid. The main differences between the five main schools of Tibetan Buddhism are not doctrinal. There are different lineages of teachings followed in each but each is in accord with the others on doctrine and there are many crossovers of lineage. The Tibetan Buddhist canon, written in English, fills several books each much bigger than the Christian Bible so I would call that a formal statement of doctrine.
Statements like "In fact, Tibetan Buddhism is a blend of Bon, a shamanistic pre-Buddhist religion and Mahayama Buddhism" are distortions. There is only a small grain of truth to that. Bon was fundamentally changed, over a long period of time, by the introduction of Buddhism to Tibet by Padmasambhava in the 8th century. Bon did influence ritual and practice in the Buddhist schools that evolved but from the start an absolute adherence to the tantric doctrine of Buddhism, brought from India at the request of the Tibetan King Tresong Detsen, has been observed to this day. The underlying principles of the Buddhist view remain intact and foundational and from what I've heard that is now true of Bon too.
What is even more troubling are your uninformed statements about Tibetan Buddhism's purity in connection with Sakymuni's original teachings. (No Buddhist I know of calls him Guatama) All schools of TB can trace an unbroken lineage of teachers to Sakymuni.
All teachings in all of these schools are in strict, unwavering accord with his teachings. The fact that other schools of Buddhism in SE Asia may say otherwise is a reflection of their lack of knowledge and understanding of tantric Buddhism not a variance in doctrine.
Sakyamuni himself predicted that an emanation of himself would come back and give his Third Basket of teachings, tantric practice, and it happened. He gave only a minimal amount of teachings on the Third Basket in his lifetime which give verification of the continuity of the teachings that came later.
The most egregious statement you made though was this IMO.
But it is certain that worship of actual deities is extremely common in Tibet itself, complete with sacrifices, even if the monks and lamas explain it away metaphirically.
There is where you stray into absolute BS. Who commanded an end to the Bon practice of animal sacrifice and when? (Even the pre-Buddhist Bon didn't do human sacrifice that I have ever heard of. You left that unclear whether intentional or not I don't know.) You don't know do you? It was Padmasambhava in the 8th century the one who established the foundation of all Buddhist practice in Tibet. There is no worship of anything or anyone in Tibetan Buddhism. Lay people may exhibit that kind of behavior but no teacher in any school on any level would agree or approve of that. Not if you conveyed an accurate understanding of what you, a westerner, mean by "worship."
Translating and getting across an accurate understanding of a word like "worship" from a western mind to a TB lama's mind, from English to Tibetan and back is not an easy thing. But I have the advantage of a relationship with an American born teacher who has had extensive relationships with several very well-respected Tibetan born lamas. His advantage is that he has achieved a level of understanding of the teachings that frees him from needing any further consultation with a teacher of his own, Tibetan or otherwise, to be clear on concepts such as worship or faith or anything else that might involve cultural or linguistic translation.
While not part and parcel of my own practice I have spent a lot of time getting clear on those things with him because I am American born and a westerner through and through so I have to filter everything I learn through a lifetime of American-western cultural thinking.
It is amazing how deeply cultural influences affect the meaning of words. Even what seem to be rather mundane words. Until you try to learn something that has originated in an entirely different culture, but at its base is not a product of any culture, that is difficult to appreciate.
Even within English speaking western culture I think there is little appreciation for the difference between 'veneration' and 'worship.' That confusion is just deepened when seeing the outward manifestations of Buddhist veneration which is quite elaborate and serious. The purpose for those kinds of ritualistic actions is very different but not readily apparent.
Knowing only a theistic mindset in the west, for that kind of behavior, I can understand that confusion. In the west those behaviors are almost exclusively associated with some kind of theistic worship. It is virtually unknown as being only a tool to train and tame the mind. The confusion is deepened because both mindsets exist in significant numbers in the east.