If the Shah lived up to his reputation of being a bloodthirsty tyrant, then Khomeini would have been dead years before 1979, and the Iranian Revolution would have taken a lot longer than January to succeed, if it even prevailed. Was the Iranian Monarchy repressive and autocratic? Absolutely. However, it was not on the same scale of brutality that succeeded it, nor of contemporary figures in the region. That being said, it was still a very dysfunctional regime that crumbled very easily.
Part of the reason the revolution happened so fast, was because the Shah was timid and cowardly. For all his bluster of being this stern authoritarian figure, he was really a reserved and shy person who had serious issues with his father in regards to his upbringing and legacy. He was more or less forced to adopt the kind of stern demeanor of his father, even though his personality was completely different, and his policy making can be seen as warped by this. Saddam Hussein was a brute, but it was his nature, and he was good at it and that made all the difference.
When the violence started to spread, and Martial law was breaking down, the Iranian Army talked about rounding up thousands of members of the Ulema, and executing them. I think the number was 10,000 or so that one general threw about. Instead, the Shah dithered, and tried to appease the revolutionaries past the 11th hour by arresting officials in SAVAK and the military, which did nothing other than sap morale among loyalists, and have key supporters of the regime waiting to be executed by the Revolutionary Tribunals after he fled. He also dragged his heels about endorsing a coup until the situation grew so badly that officers he would have relied on were already detained by Hezbollah.
The Shah could have easily tried to quell the movement like Gaddafi or Assad, but instead he chose a rather inopportune time to be moralistic about bloodshed.
As for ways in which the situation could have been prevented altogether, I will return to this thread later when I have the time.