It might be, I guess, but you can use a heat diffuser to act as a buffer. There are ones you can purchase -- sort of like trivets made of metal-covered asbestos

(last time I saw one since Woolworth's closed was in the catalogue of the Vermont Country Store). Or you can make one, by taking an empty, clean #10 can and stomping it flat.
And remember, keep the pan well-seasoned. Cast iron takes a little extra work at first, but once it's seasoned it's really easy to clean.