The big win for cast iron is its higher heat capacity. It takes longer to heat up, but once hot, the temperature drops much less when you add cold / room temperature food to fry, resulting in crisper and less soggy output.
In my experience the searing/frying performance of carbon steel is not an issue for the overwhelming majority of things I cook, ergo I don't really care that cast iron has a higher capacity. The tighter temperature control, on the other hand, is always nice.
I still use my cast irons sometimes for things where that heat capacity is really nice (searing a huge steak or something like that), but I use carbon steel much more frequently.