Just a suggestion, and one of the only examples I can think of which would be in keeping with Beedok's goal without being unashamedly ASB (although it would be a bit of a challenge to bring it about without a teensy bit of ASB assistance), would be Sikhism- which actually already comes pretty close to meeting a few of these parameters IOTL. At the dawn of the 19th century, the establishment of a unified Sikh identity, that of the Khalsa, by the last living leader of the Sikh faith, Guru Gobind Singh Ji, had barely taken place a century earlier, so it can certainly be counted as a new religion; and after Guru Gobind Singh's assassination, the Sikhs only managed to survive the Mughals' prolonged campaign of dedicated genocide by taking refuge in difficult terrain and conducting guerilla warfare, only brought to an end by Nadir Shah's Sack of Delhi in 1739. Ranjit Singh's efforts to unify the Misls (commonwealth states) of the Sikh Confederacy were already well under way, with the unification of the Empire under his rule due to take place in 1801.
At this time, most reliable sources estimate that only around 5% of the Khalsa Raj's population was Sikh. Now, IOTL, the Khalsa Raj only endured for around fifty years before being dissolved by the British, but this was long enough for the Sikhs' share of their Empire's religious demographic to skyrocket from 5% to 17%, overtaking the size of the Hindu community under their authority in this short period of time. In an ATL where the Sikh Empire endures in some shape or form (and we can more or less guarantee it'll go through some difficult times along the way, even if it manages to pull off a successful Meiji), taking into account the egalitarian policies of the religion, and the social services offered freely at all Sikh places of worship, such as the Langar community kitchens, it'd be more than feasible to imagine the Sikhs claiming a plurality within their OTL borders before the 19th century draws to a close, and becoming the majority some time in the early 20th century. As for those beyond the extent of the Sikh Empire reached IOTL, who knows? You could easily have a 'Manifest Destiny' scenario unfolding on the Indian sub-continent- Let the Singh's roar be heard, from the Persian Gulf to the Bay of Bengal...
