>but there was no shared religious tradition that held these groups together. No common books. No shared pantheon or metaphysics or theology. One Turkic steppe nomad would have wildly different beliefs to another one
Is there any folk religion that's not like this?
You're partly right about nationalists making up stuff about it, but claiming it's all made up is also absurd. It was state religion of many, including Mongols (that letter to the pope exists too)
I don't care enough to read the article, but "Kyrgyzstan and Tatarstan and to a lesser extent, in Kazakhstan, Bashkortostan and Buryatia" doesn't include Yakuts who has the most Tengrist population anyways.
Similar nearby folk religions are relevant to Shinto! But again, I don't care enough to keep discussing, nor I have a "hang up" with islam if I ever said anything about it