but yes, even all nihang dal singhs I have heard of and from agree that nirmala panth was established by guru sahiban (I can't comment on that sakhi to be frank)
I am not sure if guru sahib instructed them to partake in amrit di daat, khande bata di pahul but I would assume so (not much historical source to back my claim I admit)
nirmalay were an important ang of the broad nanakpanth and very important to parchar, but I guess since they were mostly doing parchar in eastern lands of hindus (and centers of brahmanism with haridwar, benares, and holy ganga, etc.) they slowly conformed to the ideas of same people they were preaching sikhi to in an effort to sound more inclusive and attract more sangat and slowly they eroded their principles
easy for us to condemn and criticize them, but it is hard to retain sikhi over the course of two centuries when surrounded by those following bipran ki reet
sorry for reverting such a big turn from the original topic lol