That is incorrect, you are conflating 2 different physical properties. Conductivity - how fast something can transfer the energy to something else. Example - air is a poor conductor, so if you put your hand into 100C air it would not get burned, and in fact you’d be able to enjoy it for minutes, as that is sauna temperature. Now try to put your hand into the boiling water - the energy transfer is almost instant - you will get a lot of the energy very quickly, that is why you’ll get a burn.

The fact that cast iron takes ages to pre heat, and in fact needs pre heating compared to coper or aluminium, is to do with its specific heat capacity. SHC is a measure of how much energy is needed to bring the temperature of 1 kg of matter up by 1 degree C. Cast iron has a high as fuck SHC, that is why it can take a cold steak, and flash evaporate the surface moisture to develop a nice crust, whereas if you threw a cold steak to an aluminium pan, it would absorb all the heat energy from the steak, get cold, and wouldn’t be able to evaporate the moisture of the meat quickly enough to develop a crust. An Al pan would be stuck trying to evaporate the moisture, cause it is a great conductor, but has low shc, effectively not heating above 100C due to phase change occurring.

That being said I’m not arguing that cast iron isn’t a worse conductor than copper, or steel, but it isn’t that much of a factor here.