When you learn about an important scientific discovery, does it matter to you what "line" of scientists the researcher is associated with?
When you listen to a scintillating musical performance, does it matter to you what "line" of musicians the artist is associated with?
No. At least, not much. Likely not at all.
Recently the Oregonian had a story about a classical guitarist who is going to play in Portland. It was mentioned that Scott Kritzer was the "grandson" of famed guitarist Andres Segovia, because his teacher was a Segovia student.
But that fact has no bearing on Kritzer's reputation as a guitarist, or why people are going to see him perform. He's a great guitarist. Period. That's obvious to anyone who appreciates music.
So why is it that religions, spiritual paths, and mystical practices usually are so obsessed with who gave a thumbs-up to someone else, certifying that the second person is as enlightened, God-knowledgeable, pure, or whatever other quality is important to the faith as the first person?
And so on.
Down through a lineage that might extend for a thousand years or more, as is the case with Buddhism. Also with Catholicism, which traces its Popes back to the apostle Peter. Believers are supposed to be impressed by the purported continuity of... something or other... in the faith's leaders.
Four words in that last sentence are central to the question of why lineage is so important in religiosity: something or other and faith. Because religions are focused on the supernatural, and/or on ineffable qualities of physical existence, there's no there there.
Meaning, religiosity is insubstantial, unprovable, evidence-free. In short, founded on faith. So something or other has to be taken on faith: salvation, enlightenment, god-realization, etc.
Science and art are much different.
"Show me what you've got" is the catch-phrase of scientists and artists. A discovery lacking evidence isn't a discovery. An artistic creation lacking observability isn't an artistic creation. So it's understandable why religions place so much emphasis on lineage: they've got nothing else to back up their empty claims.
Having been a member of RSSB for quite a few years, I find this sort of discussion mildly interesting from a historical perspective, yet meaningless from the perspective of whether the organization's teachings point to a transcendent truth or whether the RSSB gurus truly are "God in human form."
For that, demonstrable evidence is needed, not just proof that one guy who claimed to know a transcendent truth and supposedly was God-realized certified that his successor had those same qualities, so could take over the job of guru, so forth and so on down through an unbroken lineage.
Again, the religious obsession with lineage is a symptom of how lacking in anything supernaturally substantial religions are.
If a highly spiritual dude or dudette could perform obvious miracles, clearly foretell the future, or reliably transform the consciousness of believers into an evident more-than-human form, there wouldn't be any need for a chain of "believe me, this guy is real" testimonials from previous people with supposed spiritual accomplishments.
Since taking up dancing about six and a half years ago, my wife and I have taken lessons from quite a few different dance instructors. Our concern about who they learned how to dance from is essentially zero. What we care about is whether they know how to dance now, and can teach that to us.
It's pretty darn obvious whether someone is a good dancer. You just watch them dance. But with religion, it isn't obvious at all whether someone is a good... something or other. You see, I can't even think of what words to put after...
How can you tell whether someone is a genuine prophet, saint, guru, master, yogi, enlightened being? I have no idea. If anyone else does, please, um, enlighten me. And don't, repeat DON'T, describe some quality of a human being which could apply to any non-religious person.
Like: kind, compassionate, wise, charismatic, giving, selfless, inspiring, loving. I know lots of atheists and agnostics who have these qualities.
And also don't tell me that genuine spirituality is demonstrated by getting a stamp of approval from some other supposed genuine spiritual person. I need to know how it's possible to discern the genuineness of the first genuine spiritual person.
Bottom line: with religions, don't trust lineages. Don't care about lineages. Be like a scientist or artist. Say "show me what you've got." Now.