True, but with the snowballing, he won't really need friends that much. As for his unhappiness, it seems quite manageable for the AI on immortal, and he won't have such an unhappiness problems if he found just a few of his cities and then goes bullying, because he won't have many undeveloped cities, but most of his empire will consist of former CS with a good infrastructure, CS-unique-luxuries etc.
But if the AI testing games don't show him to be OP, then I'm okay with Mongolia remaining unchanged, I can always ensure Genghis is not in the game.