I agree wholeheartedly with His Holiness the 17th Karmapa when he says it is most important to keep one’s samaya with the root Guru. I was once told a story where a dedicated and educated practitioner emerged after several years of retreat and went to his Lineage Master to complain of his lack of progress.
The Guru sent the retreatant back to the cave, saying five more years were needed. In five years this happened again. This time the Guru said, concentrate on the Root Guru! So the practitioner went back for five more years. Still almost no result! No Bodhicitta, no Wisdom or Recognition. The Guru then shouted, “You did not meditate on your root Guru!”
“Well,” said student “I most certainly did.” The High Lama said, “I am not your root Guru! I am one of your teachers and you favor me because I have a high throne! That makes you feel that you certainly are high yourself!”
The great lama in his clarity and mercy said, “You fool! The old poor Ani who fed, raised and dressed you also taught you the four contemplations that turn the mind to Dharma, as well as Bodhicitta, the Four Noble Truths, including the Eight-Fold Path! How stupid and arrogant to think you must have the highest Lama! Such pride! A downfall! So go back and meditate on mixing your mind with that old ragged Ani. She is your Tsawei Lama and was also a wisdom Dakini. Her Qualities were peerless, sublime! But pride has closed your eyes.” Then with fury he cast the practitioner away, saying, “Come back when you have thrown away your pride.”
Five years later the retreatant returned with gifts and prostrations. He was, much to the delight of the Great Lama, awake. He had mixed his mind with his true Guru, had given rise to pure Bodhicitta, and had no pride.
Both the Great Lama and the disciple rejoiced together, and could hear the joyous cries of the wisdom Dakini throughout the entire monastery- Kye Ho!
So the Root Guru only needs to be awakened herself, be able to communicate, and have lineage teachings to pass on. “High Seats” are another issue entirely. It is that one who hooks and aligns you with pure Dharma, connects you with method and result who is the true Root Guru. Praise to the Root of Accomplishment!