Of course. Look around, humanity can maintain innumerable stupid and harmful traditions.
I said valid. For a stupid and harmful tradition to be maintained it must mean that there is some validity and/or value to it. Maybe not the type of validity and value that you consider intelligent and helpful but...
Since it is obvious that the teachings are taken from Buddhism while they claim to have their own ancient lineage going back to thousands of years, naturally the lineage is a made up myth.
Do you think "Buddhists" have a monopoly on some techniques/practices? And I think you will find that Bon practitioners recognise which techniques are/were Buddhist and which were Bon. If a Christian takes, let's say, guru yoga and practices using the figure of Christ as a guru and due to the effectivenes of the technique it is adopted by Christians would this mean that the technique is Christian? Does it mean that the Christian lineage is now broken? Does it mean that the thread of the Buddhist lineage is broken?
If someone doesn't believe in the teachings, the person doesn't believe in the lineage either. If they believe the teachings then it doesn't matter what lineage it is.
So how did they receive the teachings if the lineage is irrelevant? It fell out of the sky? If the individual thinks that the technique/practice starts and ends with them, then that, my friend, is just egotistical pride. Check out this teaching
So how does a lineage verifies a practice?
Firstly, you misunderstood what I meant. I meant that, well I'll give an example: Let's say I had a sudden flash and insight and vision etc... and happened to be chewing on some grape flavoured chewing gum when it happened. So I consider the chewing gum as the source of my insight and vision and make a practice around the chewing of gum. If I belong to an established lineage, I can take this practice to somebody more qualified and realised than me, within the lineage, and tell them about my amazing practice and experience and then they can verify... If you do not belong to an established lineage...?
Something that worked for others doesn't mean it will work for me or a different group of people.
This is not 100% correct. There are actually some practices (Anapanasati, for example) that work for everybody. And, anyway, Budhism is not psychoanalysis, it's not me, me, me, me... Lojong is a perfect example of this point.
Even in Buddhism, what makes you choose one lineage instead of the other, if what is important is the existence of a lineage?
Karmic proclitivty makes you choose one lineage over another, nothing else. Thankfully, though, some individuals, over the course of history, decided to pass on the techniques so that we now have the privilege of being able to "choose". It was due to their efforts to maintain a lineage of transmission that we now have the benefit of having the practices available.