Y Not,
“and Buddha Dhamma is that only in the latter is found a way out of life’s sufferings.” Which is terribly important, it’s of a vertiginous deepness.
“those Yogis and Gurus resposonsible for these teachings actually retrieved them from fragments of the Buddha Kassapa sasana – of course, with their own views and other additions to it throughout the time since.” Quite probably,yes, i wouldn’t be surprised.