Lama Atisha famously brought the teachings of Nalanda back to Tibet and authored his famous, A Lamp for the Path to Enlightenment upon which the new translation schools were founded. This seminal text is the foundational document of the lamrim upon which all subsequent lamrims are based.
Atisha did not seem to mention guru devotion in his lamrim. Spiritual teachers are mentioned only in the course of explaining how to properly receive the Bodhisattva vows and to receive Tantric initiations. Nowhere can I find the idea that guru devotion is the root of the path to enlightenment.
Je Tsongkhapa on the other hand listed guru devotion towards the very beginning of his lamrim and it is widely taught in new translation schools that guru devotion is the root of the path to enlightenment. Why is this? Why would something so important and fundamental be left out entirely by Lama Atisha from his seminal text?
Also, this is what His Holiness the Dalai Lama has said about guru devotion in Questioning the Advice of the Guru:
It is frequently said that the essence of the training in guru yoga is to cultivate the art of seeing everything the guru does as perfect. Personally I myself do not like this to be taken too far. Often we see written in the scriptures, “Every action seen as perfect.” However, this phrase must be seen in the light of Buddha Shakyamuni’s own words: “Accept my teachings only after examining them as an analyst buys gold. Accept nothing out of mere faith in me.” The problem with the practice of seeing everything the guru does as perfect is that it very easily turns to poison for both the guru and the disciple. Therefore, whenever I teach this practice, I always advocate that the tradition of “every action seen as perfect” not be stressed. Should the guru manifest unDharmic qualities or give teachings contradicting Dharma, the instruction on seeing the spiritual master as perfect must give way to reason and Dharma wisdom.
Perhaps you will think: “The Dalai Lama has not read the Lam Rim scriptures. He does not know that there is no practice of Dharma without the guru.” I am not being disrespectful of the Lam Rim teachings. A student of the spiritual path should rely upon a teacher and should meditate on that teacher’s kindness and good qualities; but the teaching on seeing his or her actions as perfect can only be applied within the context of the Dharma as a whole and the rational approach to knowledge that it advocates. As the teachings on seeing the guru’s actions as perfect is borrowed from Highest Tantra and appears in the Lam Rim mainly to prepare the trainee for tantric practice, beginners must treat it with caution. As for spiritual teachers, if they misrepresent this precept of guru yoga in order to take advantage of naive disciples, their actions are like pouring the liquid fires of hell directly into their stomachs.
Emphasis mine. If preparing the trainee for Tantric practice is the reason for adding it to the Lamrim, then is it true that guru devotion is not of such importance for those studying sutra only? In other words, can it be said that for those practicing sutrayana only that guru devotion is not the root of the path?