Well, there you go. I don't know that I really need to bother too much with slotting him in other cities, save for a couple of mid-tier promotions.
Yes, Carl seemed to be doing a pretty effective conquest using Ibrahim, catapults, and upgrading swordsmen into janissaries.
I suppose once the war is over you might put him in an opponents city to protect your conquests from loyalty pressure, at least until you go to war again.