Historically, incendiary bombs where much less effective against European targets then they were in the Pacific, due to the more solid nature of the structures. People will point out Dresden as a counter-example, but the fire bombs only did their intended job after much of Dresden was reduced to wreckage, which caught, burned, and spread much more easily. The bombs themselves had a somewhat limited radius of effectiveness. Even when used in Europe, it was typically to mix incendiary and HE bombs in the same raid. The dynamics of real-life would be hard to model in AH, I think. A friend of mine, Daniel Schwabe, wrote a great book on the fire bombing of Japan, discussing the how and why it was effective there. The title is "Burning Japan: Air Force Bombing Strategy Change in the Pacific"(
https://www.amazon.com/Burning-Japan-Bombing-Strategy-Pacific/dp/1612346391). Regardless, they're not the universally effective wonder-weapon you believe they are.