What makes you say that Sunni Mongols mean doom? Now they can only declare invasions if they save 1000 piety. Admittedly that guy is almost there.
Yes, but there is another problem. The world at the start was shattered into counts ( Part of the HIP Mod decions once you start a game ). So there is no empire besides the Persian Empire that could stand up to the Mongol horde but they did not do a good job. Right now defensive pacts are the only things slowing them down.. But even still his doom stacks are still around.
It will make for an interesting story to see how the world recovers when the Mongols empire splits up and hopefully it happens.. Since the only thing really standing in the way of the Mongol empire is the defensive pact.