1. Egyption, Greek, and Roman religions also had people believing in them for long periods of time. There have been many religions (and still are) that have lasted for long periods time. The length of time a religion has been around is not a real good metric.
2. Also not a good metric, especially since it's only been around for a relatively short period of. Religions don't appear with people already divided.
3. And that's different from other religions because...?
The simple fact is a religion is whatever you believe it to be. One person's pink unicorn worship is no sillier than a million people worshiping invisible sky fairies. Religion is in the eye of the beholder.
All religions are abusive and used like any tool for power, wealth, etc. . The only real difference is that Scientology is basically coming right out and screaming it's scam unlike most other main stream religions who do it far more subtly.