>That does not make "traditions flexible". It's just a cheap tactic to increase followers/harvest souls.

That's not mutually exclusive. You're certainly right that religions spread this way, but it's also what they become. Christians today are Pauline Christians more than anything else. The abolition of circumcision and dietary restrictions, household code, 'render unto Caesear' etc were obviously tactics to convert Gentiles, but once you had all the gentiles, you had genuinely altered what the faith is. They never went back to the radicalism of Jesus.

Buddhism is also an interesting case. By the start of the 19th century there wasn't strong Buddhist practice in India. When it was rediscovered it was heavily shaped by China, Tibet and Japan and had done a round about turn.

Same with modern Evangelicalism and Catholicism. Very successfully spread through indigenous cultures in LatAm and Africa but now the influence goes the other way, with real impact on the churches, just look at the last two popes. I don't think this deserves to be categorized as cheap tactic, that's very much what religion is.