To me a cult means having total control over people's lives. This has evolved gradually. We had Russell predicting dates that didn't bring Armageddon. I agree he didn't mean to start a cult but other leaders followed him and the end didn't come so they demanded total obedience, unquestioning loyalty in the face of failed prophecies.
The GB seem to think any loosening of the bonds of obedience to doctrine and lifestyle rules would mean the religon would collapse. Also rewriting the history of the Borg and getting rid of old literature so they're living in a time warp.